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Anatomy_Gray_1000	Anatomy_Gray	Three apertures in the pelvic wall communicate with the lower limb (Fig. 5.10A): the obturator canal, the greater sciatic foramen, and the lesser sciatic foramen. The obturator canal forms a passageway between the pelvic cavity and the adductor region of the thigh, and is formed in the superior aspect of the obturator foramen, between bone, a connective tissue membrane, and muscles that fill the foramen. The lesser sciatic foramen, which lies inferior to the pelvic floor, provides communication between the gluteal region and the perineum (Fig. 5.10B). The pelvic cavity also communicates directly with the perineum through a small gap between the pubic symphysis and the perineal membrane (Fig. 5.10B). The pelvic cavity projects posteriorly	Anatomy_Gray. Three apertures in the pelvic wall communicate with the lower limb (Fig. 5.10A): the obturator canal, the greater sciatic foramen, and the lesser sciatic foramen. The obturator canal forms a passageway between the pelvic cavity and the adductor region of the thigh, and is formed in the superior aspect of the obturator foramen, between bone, a connective tissue membrane, and muscles that fill the foramen. The lesser sciatic foramen, which lies inferior to the pelvic floor, provides communication between the gluteal region and the perineum (Fig. 5.10B). The pelvic cavity also communicates directly with the perineum through a small gap between the pubic symphysis and the perineal membrane (Fig. 5.10B). The pelvic cavity projects posteriorly
Anatomy_Gray_1001	Anatomy_Gray	The pelvic cavity also communicates directly with the perineum through a small gap between the pubic symphysis and the perineal membrane (Fig. 5.10B). The pelvic cavity projects posteriorly In the anatomical position, the anterior superior iliac spines and the superior edge of the pubic symphysis lie in the same vertical plane (Fig. 5.11). Consequently, the pelvic inlet is angled 50°–60° forward relative to the horizontal plane, and the pelvic cavity projects posteriorly from the abdominal cavity. Meanwhile, the urogenital part of the pelvic outlet (the pubic arch) is oriented in a nearly horizontal plane, whereas the posterior part of the outlet is positioned more vertically. The urogenital triangle of the perineum therefore faces inferiorly, while the anal triangle faces more posteriorly. Important structures cross the ureters in the pelvic cavity	Anatomy_Gray. The pelvic cavity also communicates directly with the perineum through a small gap between the pubic symphysis and the perineal membrane (Fig. 5.10B). The pelvic cavity projects posteriorly In the anatomical position, the anterior superior iliac spines and the superior edge of the pubic symphysis lie in the same vertical plane (Fig. 5.11). Consequently, the pelvic inlet is angled 50°–60° forward relative to the horizontal plane, and the pelvic cavity projects posteriorly from the abdominal cavity. Meanwhile, the urogenital part of the pelvic outlet (the pubic arch) is oriented in a nearly horizontal plane, whereas the posterior part of the outlet is positioned more vertically. The urogenital triangle of the perineum therefore faces inferiorly, while the anal triangle faces more posteriorly. Important structures cross the ureters in the pelvic cavity
Anatomy_Gray_1002	Anatomy_Gray	Important structures cross the ureters in the pelvic cavity The ureters drain the kidneys, course down the posterior abdominal wall, and cross the pelvic inlet to enter the pelvic cavity. They continue inferiorly along the lateral pelvic wall and ultimately connect with the base of the bladder. An important structure crosses the ureters in the pelvic cavity in both men and women—in women, the uterine artery crosses the ureter lateral to the cervix of the uterus (Fig. 5.12A), and in men, the ductus deferens crosses over the ureter just posterior to the bladder (Fig. 5.12B). The prostate in men and the uterus in women are anterior to the rectum In men, the prostate gland is situated immediately anterior to the rectum, just above the pelvic floor (Fig. 5.13). It can be felt by digital palpation during a rectal examination.	Anatomy_Gray. Important structures cross the ureters in the pelvic cavity The ureters drain the kidneys, course down the posterior abdominal wall, and cross the pelvic inlet to enter the pelvic cavity. They continue inferiorly along the lateral pelvic wall and ultimately connect with the base of the bladder. An important structure crosses the ureters in the pelvic cavity in both men and women—in women, the uterine artery crosses the ureter lateral to the cervix of the uterus (Fig. 5.12A), and in men, the ductus deferens crosses over the ureter just posterior to the bladder (Fig. 5.12B). The prostate in men and the uterus in women are anterior to the rectum In men, the prostate gland is situated immediately anterior to the rectum, just above the pelvic floor (Fig. 5.13). It can be felt by digital palpation during a rectal examination.
Anatomy_Gray_1003	Anatomy_Gray	In men, the prostate gland is situated immediately anterior to the rectum, just above the pelvic floor (Fig. 5.13). It can be felt by digital palpation during a rectal examination. In both sexes, the anal canal and the lower rectum also can be evaluated during a rectal examination by a clinician. In women, the cervix and lower part of the body of the uterus also are palpable. However, these structures can more easily be palpated with a bimanual examination where the index and middle fingers of a clinician’s hand are placed in the vagina and the other hand is placed on the lower anterior abdominal wall. The organs are felt between the two hands. This bimanual technique can also be used to examine the ovaries and uterine tubes. The perineum is innervated by sacral spinal	Anatomy_Gray. In men, the prostate gland is situated immediately anterior to the rectum, just above the pelvic floor (Fig. 5.13). It can be felt by digital palpation during a rectal examination. In both sexes, the anal canal and the lower rectum also can be evaluated during a rectal examination by a clinician. In women, the cervix and lower part of the body of the uterus also are palpable. However, these structures can more easily be palpated with a bimanual examination where the index and middle fingers of a clinician’s hand are placed in the vagina and the other hand is placed on the lower anterior abdominal wall. The organs are felt between the two hands. This bimanual technique can also be used to examine the ovaries and uterine tubes. The perineum is innervated by sacral spinal
Anatomy_Gray_1004	Anatomy_Gray	The perineum is innervated by sacral spinal Dermatomes of the perineum in both men and women are from spinal cord levels S3 to S5, except for the anterior regions, which tend to be innervated by spinal cord level L1 by nerves associated with the abdominal wall (Fig. 5.14). Dermatomes of L2 to S2 are predominantly in the lower limb. Most of the skeletal muscles contained in the perineum and the pelvic floor, including the external anal sphincter and external urethral sphincter, are innervated by spinal cord levels S2 to S4. Much of the somatic motor and sensory innervation of the perineum is provided by the pudendal nerve from spinal cord levels S2 to S4. Nerves are related to bone	Anatomy_Gray. The perineum is innervated by sacral spinal Dermatomes of the perineum in both men and women are from spinal cord levels S3 to S5, except for the anterior regions, which tend to be innervated by spinal cord level L1 by nerves associated with the abdominal wall (Fig. 5.14). Dermatomes of L2 to S2 are predominantly in the lower limb. Most of the skeletal muscles contained in the perineum and the pelvic floor, including the external anal sphincter and external urethral sphincter, are innervated by spinal cord levels S2 to S4. Much of the somatic motor and sensory innervation of the perineum is provided by the pudendal nerve from spinal cord levels S2 to S4. Nerves are related to bone
Anatomy_Gray_1005	Anatomy_Gray	Much of the somatic motor and sensory innervation of the perineum is provided by the pudendal nerve from spinal cord levels S2 to S4. Nerves are related to bone The pudendal nerve is the major nerve of the perineum and is directly associated with the ischial spine of the pelvis (Fig. 5.15). On each side of the body, these spines and the attached sacrospinous ligaments separate the greater sciatic foramina from the lesser sciatic foramina on the lateral pelvic wall. The pudendal nerve leaves the pelvic cavity through the greater sciatic foramen and then immediately enters the perineum inferiorly to the pelvic floor by passing around the ischial spine and through the lesser sciatic foramen (Fig. 5.15). The ischial spine can be palpated transvaginally in women and is the landmark that can be used for administering a pudendal nerve block. Parasympathetic innervation from spinal cord levels S2 to S4 controls erection	Anatomy_Gray. Much of the somatic motor and sensory innervation of the perineum is provided by the pudendal nerve from spinal cord levels S2 to S4. Nerves are related to bone The pudendal nerve is the major nerve of the perineum and is directly associated with the ischial spine of the pelvis (Fig. 5.15). On each side of the body, these spines and the attached sacrospinous ligaments separate the greater sciatic foramina from the lesser sciatic foramina on the lateral pelvic wall. The pudendal nerve leaves the pelvic cavity through the greater sciatic foramen and then immediately enters the perineum inferiorly to the pelvic floor by passing around the ischial spine and through the lesser sciatic foramen (Fig. 5.15). The ischial spine can be palpated transvaginally in women and is the landmark that can be used for administering a pudendal nerve block. Parasympathetic innervation from spinal cord levels S2 to S4 controls erection
Anatomy_Gray_1006	Anatomy_Gray	Parasympathetic innervation from spinal cord levels S2 to S4 controls erection The parasympathetic innervation from spinal cord levels S2 to S4 controls genital erection in both women and men (Fig. 5.16). On each side, preganglionic parasympathetic nerves leave the anterior rami of the sacral spinal nerves and enter the inferior hypogastric plexus (pelvic plexus) on the lateral pelvic wall. The two inferior hypogastric plexuses are inferior extensions of the abdominal prevertebral plexus that forms on the posterior abdominal wall in association with the abdominal aorta. Nerves derived from these plexuses penetrate the pelvic floor to innervate the erectile tissues of the clitoris in women and the penis in men. Muscles and fascia of the pelvic floor and perineum intersect at the perineal body	Anatomy_Gray. Parasympathetic innervation from spinal cord levels S2 to S4 controls erection The parasympathetic innervation from spinal cord levels S2 to S4 controls genital erection in both women and men (Fig. 5.16). On each side, preganglionic parasympathetic nerves leave the anterior rami of the sacral spinal nerves and enter the inferior hypogastric plexus (pelvic plexus) on the lateral pelvic wall. The two inferior hypogastric plexuses are inferior extensions of the abdominal prevertebral plexus that forms on the posterior abdominal wall in association with the abdominal aorta. Nerves derived from these plexuses penetrate the pelvic floor to innervate the erectile tissues of the clitoris in women and the penis in men. Muscles and fascia of the pelvic floor and perineum intersect at the perineal body
Anatomy_Gray_1007	Anatomy_Gray	Muscles and fascia of the pelvic floor and perineum intersect at the perineal body Structures of the pelvic floor intersect with structures in the perineum at the perineal body (Fig. 5.17). This poorly defined fibromuscular node lies at the center of the perineum, approximately midway between the two ischial tuberosities. Converging at the perineal body are: the levator ani muscles of the pelvic diaphragm, and muscles in the urogenital and anal triangles of the perineum, including the skeletal muscle sphincters associated with the urethra, vagina, and anus. The course of the urethra is different in men In women, the urethra is short and passes inferiorly from the bladder through the pelvic floor and opens directly into the perineum (Fig. 5.18A).	Anatomy_Gray. Muscles and fascia of the pelvic floor and perineum intersect at the perineal body Structures of the pelvic floor intersect with structures in the perineum at the perineal body (Fig. 5.17). This poorly defined fibromuscular node lies at the center of the perineum, approximately midway between the two ischial tuberosities. Converging at the perineal body are: the levator ani muscles of the pelvic diaphragm, and muscles in the urogenital and anal triangles of the perineum, including the skeletal muscle sphincters associated with the urethra, vagina, and anus. The course of the urethra is different in men In women, the urethra is short and passes inferiorly from the bladder through the pelvic floor and opens directly into the perineum (Fig. 5.18A).
Anatomy_Gray_1008	Anatomy_Gray	The course of the urethra is different in men In women, the urethra is short and passes inferiorly from the bladder through the pelvic floor and opens directly into the perineum (Fig. 5.18A). In men the urethra passes through the prostate before coursing through the deep perineal pouch and perineal membrane and then becomes enclosed within the erectile tissues of the penis before opening at the end of the penis (Fig. 5.18B). The penile part of the male urethra has two angles: The more important of these is a fixed angle where the urethra bends anteriorly in the root of the penis after passing through the perineal membrane. Another angle occurs distally where the unattached part of the penis curves inferiorly—when the penis is erect, this second angle disappears. It is important to consider the different courses of the urethra in men and women when catheterizing patients and when evaluating perineal injuries and pelvic pathology.	Anatomy_Gray. The course of the urethra is different in men In women, the urethra is short and passes inferiorly from the bladder through the pelvic floor and opens directly into the perineum (Fig. 5.18A). In men the urethra passes through the prostate before coursing through the deep perineal pouch and perineal membrane and then becomes enclosed within the erectile tissues of the penis before opening at the end of the penis (Fig. 5.18B). The penile part of the male urethra has two angles: The more important of these is a fixed angle where the urethra bends anteriorly in the root of the penis after passing through the perineal membrane. Another angle occurs distally where the unattached part of the penis curves inferiorly—when the penis is erect, this second angle disappears. It is important to consider the different courses of the urethra in men and women when catheterizing patients and when evaluating perineal injuries and pelvic pathology.
Anatomy_Gray_1009	Anatomy_Gray	It is important to consider the different courses of the urethra in men and women when catheterizing patients and when evaluating perineal injuries and pelvic pathology. The pelvis is the region of the body surrounded by the pelvic bones and the inferior elements of the vertebral column. It is divided into two major regions: the superior region is the false (greater) pelvis and is part of the abdominal cavity; the inferior region is the true (lesser) pelvis, which encloses the pelvic cavity. The bowl-shaped pelvic cavity is continuous above with the abdominal cavity. The rim of the pelvic cavity (the pelvic inlet) is completely encircled by bone. The pelvic floor is a fibromuscular structure separating the pelvic cavity above from the perineum below.	Anatomy_Gray. It is important to consider the different courses of the urethra in men and women when catheterizing patients and when evaluating perineal injuries and pelvic pathology. The pelvis is the region of the body surrounded by the pelvic bones and the inferior elements of the vertebral column. It is divided into two major regions: the superior region is the false (greater) pelvis and is part of the abdominal cavity; the inferior region is the true (lesser) pelvis, which encloses the pelvic cavity. The bowl-shaped pelvic cavity is continuous above with the abdominal cavity. The rim of the pelvic cavity (the pelvic inlet) is completely encircled by bone. The pelvic floor is a fibromuscular structure separating the pelvic cavity above from the perineum below.
Anatomy_Gray_1010	Anatomy_Gray	The perineum is inferior to the pelvic floor and its margin is formed by the pelvic outlet. The perineum contains: the terminal openings of the gastrointestinal and urinary systems, the external opening of the reproductive tract, and the roots of the external genitalia. The bones of the pelvis consist of the right and left pelvic (hip) bones, the sacrum, and the coccyx. The sacrum articulates superiorly with vertebra LV at the lumbosacral joint. The pelvic bones articulate posteriorly with the sacrum at the sacro-iliac joints and with each other anteriorly at the pubic symphysis. The pelvic bone is irregular in shape and has two major parts separated by an oblique line on the medial surface of the bone (Fig. 5.19A): The pelvic bone above this line represents the lateral wall of the false pelvis, which is part of the abdominal cavity. The pelvic bone below this line represents the lateral wall of the true pelvis, which contains the pelvic cavity.	Anatomy_Gray. The perineum is inferior to the pelvic floor and its margin is formed by the pelvic outlet. The perineum contains: the terminal openings of the gastrointestinal and urinary systems, the external opening of the reproductive tract, and the roots of the external genitalia. The bones of the pelvis consist of the right and left pelvic (hip) bones, the sacrum, and the coccyx. The sacrum articulates superiorly with vertebra LV at the lumbosacral joint. The pelvic bones articulate posteriorly with the sacrum at the sacro-iliac joints and with each other anteriorly at the pubic symphysis. The pelvic bone is irregular in shape and has two major parts separated by an oblique line on the medial surface of the bone (Fig. 5.19A): The pelvic bone above this line represents the lateral wall of the false pelvis, which is part of the abdominal cavity. The pelvic bone below this line represents the lateral wall of the true pelvis, which contains the pelvic cavity.
Anatomy_Gray_1011	Anatomy_Gray	The pelvic bone below this line represents the lateral wall of the true pelvis, which contains the pelvic cavity. The linea terminalis is the lower two-thirds of this line and contributes to the margin of the pelvic inlet. The lateral surface of the pelvic bone has a large articular socket, the acetabulum, which, together with the head of the femur, forms the hip joint (Fig. 5.19B). Inferior to the acetabulum is the large obturator foramen, most of which is closed by a flat connective tissue membrane, the obturator membrane. A small obturator canal remains open superiorly between the membrane and adjacent bone, providing a route of communication between the lower limb and the pelvic cavity. The posterior margin of the bone is marked by two notches separated by the ischial spine: the greater sciatic notch, and the lesser sciatic notch. The posterior margin terminates inferiorly as the large ischial tuberosity.	Anatomy_Gray. The pelvic bone below this line represents the lateral wall of the true pelvis, which contains the pelvic cavity. The linea terminalis is the lower two-thirds of this line and contributes to the margin of the pelvic inlet. The lateral surface of the pelvic bone has a large articular socket, the acetabulum, which, together with the head of the femur, forms the hip joint (Fig. 5.19B). Inferior to the acetabulum is the large obturator foramen, most of which is closed by a flat connective tissue membrane, the obturator membrane. A small obturator canal remains open superiorly between the membrane and adjacent bone, providing a route of communication between the lower limb and the pelvic cavity. The posterior margin of the bone is marked by two notches separated by the ischial spine: the greater sciatic notch, and the lesser sciatic notch. The posterior margin terminates inferiorly as the large ischial tuberosity.
Anatomy_Gray_1012	Anatomy_Gray	The posterior margin terminates inferiorly as the large ischial tuberosity. The irregular anterior margin of the pelvic bone is marked by the anterior superior iliac spine, the anterior inferior iliac spine, and the pubic tubercle. Components of the pelvic bone Each pelvic bone is formed by three elements: the ilium, pubis, and ischium. At birth, these bones are connected by cartilage in the area of the acetabulum; later, at between 16 and 18 years of age, they fuse into a single bone (Fig. 5.20). Of the three components of the pelvic bone, the ilium is the most superior in position. The ilium is separated into upper and lower parts by a ridge on the medial surface (Fig. 5.21A).	Anatomy_Gray. The posterior margin terminates inferiorly as the large ischial tuberosity. The irregular anterior margin of the pelvic bone is marked by the anterior superior iliac spine, the anterior inferior iliac spine, and the pubic tubercle. Components of the pelvic bone Each pelvic bone is formed by three elements: the ilium, pubis, and ischium. At birth, these bones are connected by cartilage in the area of the acetabulum; later, at between 16 and 18 years of age, they fuse into a single bone (Fig. 5.20). Of the three components of the pelvic bone, the ilium is the most superior in position. The ilium is separated into upper and lower parts by a ridge on the medial surface (Fig. 5.21A).
Anatomy_Gray_1013	Anatomy_Gray	Of the three components of the pelvic bone, the ilium is the most superior in position. The ilium is separated into upper and lower parts by a ridge on the medial surface (Fig. 5.21A). Posteriorly, the ridge is sharp and lies immediately superior to the surface of the bone that articulates with the sacrum. This sacral surface has a large L-shaped facet for articulating with the sacrum and an expanded, posterior roughened area for the attachment of the strong ligaments that support the sacro-iliac joint (Fig. 5.21). Anteriorly, the ridge separating the upper and lower parts of the ilium is rounded and termed the arcuate line. The arcuate line forms part of the linea terminalis and the pelvic brim. The portion of the ilium lying inferiorly to the arcuate line is the pelvic part of the ilium and contributes to the wall of the lesser or true pelvis.	Anatomy_Gray. Of the three components of the pelvic bone, the ilium is the most superior in position. The ilium is separated into upper and lower parts by a ridge on the medial surface (Fig. 5.21A). Posteriorly, the ridge is sharp and lies immediately superior to the surface of the bone that articulates with the sacrum. This sacral surface has a large L-shaped facet for articulating with the sacrum and an expanded, posterior roughened area for the attachment of the strong ligaments that support the sacro-iliac joint (Fig. 5.21). Anteriorly, the ridge separating the upper and lower parts of the ilium is rounded and termed the arcuate line. The arcuate line forms part of the linea terminalis and the pelvic brim. The portion of the ilium lying inferiorly to the arcuate line is the pelvic part of the ilium and contributes to the wall of the lesser or true pelvis.
Anatomy_Gray_1014	Anatomy_Gray	The portion of the ilium lying inferiorly to the arcuate line is the pelvic part of the ilium and contributes to the wall of the lesser or true pelvis. The upper part of the ilium expands to form a flat, fan-shaped “wing,” which provides bony support for the lower abdomen, or false pelvis. This part of the ilium provides attachment for muscles functionally associated with the lower limb. The anteromedial surface of the wing is concave and forms the iliac fossa. The external (gluteal) surface of the wing is marked by lines and roughenings and is related to the gluteal region of the lower limb (Fig. 5.21B). The entire superior margin of the ilium is thickened to form a prominent crest (the iliac crest), which is the site of attachment for muscles and fascia of the abdomen, back, and lower limb and terminates anteriorly as the anterior superior iliac spine and posteriorly as the posterior superior iliac spine.	Anatomy_Gray. The portion of the ilium lying inferiorly to the arcuate line is the pelvic part of the ilium and contributes to the wall of the lesser or true pelvis. The upper part of the ilium expands to form a flat, fan-shaped “wing,” which provides bony support for the lower abdomen, or false pelvis. This part of the ilium provides attachment for muscles functionally associated with the lower limb. The anteromedial surface of the wing is concave and forms the iliac fossa. The external (gluteal) surface of the wing is marked by lines and roughenings and is related to the gluteal region of the lower limb (Fig. 5.21B). The entire superior margin of the ilium is thickened to form a prominent crest (the iliac crest), which is the site of attachment for muscles and fascia of the abdomen, back, and lower limb and terminates anteriorly as the anterior superior iliac spine and posteriorly as the posterior superior iliac spine.
Anatomy_Gray_1015	Anatomy_Gray	A prominent tubercle, the tuberculum of the iliac crest, projects laterally near the anterior end of the crest; the posterior end of the crest thickens to form the iliac tuberosity. Inferior to the anterior superior iliac spine of the crest, on the anterior margin of the ilium, is a rounded protuberance called the anterior inferior iliac spine. This structure serves as the point of attachment for the rectus femoris muscle of the anterior compartment of the thigh and the iliofemoral ligament associated with the hip joint. A less prominent posterior inferior iliac spine occurs along the posterior border of the sacral surface of the ilium, where the bone angles forward to form the superior margin of the greater sciatic notch. The anterior and inferior part of the pelvic bone is the pubis (Fig. 5.21). It has a body and two arms (rami).	Anatomy_Gray. A prominent tubercle, the tuberculum of the iliac crest, projects laterally near the anterior end of the crest; the posterior end of the crest thickens to form the iliac tuberosity. Inferior to the anterior superior iliac spine of the crest, on the anterior margin of the ilium, is a rounded protuberance called the anterior inferior iliac spine. This structure serves as the point of attachment for the rectus femoris muscle of the anterior compartment of the thigh and the iliofemoral ligament associated with the hip joint. A less prominent posterior inferior iliac spine occurs along the posterior border of the sacral surface of the ilium, where the bone angles forward to form the superior margin of the greater sciatic notch. The anterior and inferior part of the pelvic bone is the pubis (Fig. 5.21). It has a body and two arms (rami).
Anatomy_Gray_1016	Anatomy_Gray	The anterior and inferior part of the pelvic bone is the pubis (Fig. 5.21). It has a body and two arms (rami). The body is flattened dorsoventrally and articulates with the body of the pubic bone on the other side at the pubic symphysis. The body has a rounded pubic crest on its superior surface that ends laterally as the prominent pubic tubercle. The superior pubic ramus projects posterolaterally from the body and joins with the ilium and ischium at its base, which is positioned toward the acetabulum. The sharp superior margin of this triangular surface is termed the pecten pubis (pectineal line), which forms part of the linea terminalis of the pelvic bone and the pelvic inlet. Anteriorly, this line is continuous with the pubic crest, which also is part of the linea terminalis and pelvic inlet. The superior pubic ramus is marked on its inferior surface by the obturator groove, which forms the upper margin of the obturator canal.	Anatomy_Gray. The anterior and inferior part of the pelvic bone is the pubis (Fig. 5.21). It has a body and two arms (rami). The body is flattened dorsoventrally and articulates with the body of the pubic bone on the other side at the pubic symphysis. The body has a rounded pubic crest on its superior surface that ends laterally as the prominent pubic tubercle. The superior pubic ramus projects posterolaterally from the body and joins with the ilium and ischium at its base, which is positioned toward the acetabulum. The sharp superior margin of this triangular surface is termed the pecten pubis (pectineal line), which forms part of the linea terminalis of the pelvic bone and the pelvic inlet. Anteriorly, this line is continuous with the pubic crest, which also is part of the linea terminalis and pelvic inlet. The superior pubic ramus is marked on its inferior surface by the obturator groove, which forms the upper margin of the obturator canal.
Anatomy_Gray_1017	Anatomy_Gray	The inferior ramus projects laterally and inferiorly to join with the ramus of the ischium. The ischium is the posterior and inferior part of the pelvic bone (Fig. 5.21). It has: a large body that projects superiorly to join with the ilium and the superior ramus of the pubis, and a ramus that projects anteriorly to join with the inferior ramus of the pubis. The posterior margin of the bone is marked by a prominent ischial spine that separates the lesser sciatic notch, below, from the greater sciatic notch, above. The most prominent feature of the ischium is a large tuberosity (the ischial tuberosity) on the posteroinferior aspect of the bone. This tuberosity is an important site for the attachment of lower limb muscles and for supporting the body when sitting.	Anatomy_Gray. The inferior ramus projects laterally and inferiorly to join with the ramus of the ischium. The ischium is the posterior and inferior part of the pelvic bone (Fig. 5.21). It has: a large body that projects superiorly to join with the ilium and the superior ramus of the pubis, and a ramus that projects anteriorly to join with the inferior ramus of the pubis. The posterior margin of the bone is marked by a prominent ischial spine that separates the lesser sciatic notch, below, from the greater sciatic notch, above. The most prominent feature of the ischium is a large tuberosity (the ischial tuberosity) on the posteroinferior aspect of the bone. This tuberosity is an important site for the attachment of lower limb muscles and for supporting the body when sitting.
Anatomy_Gray_1018	Anatomy_Gray	The sacrum, which has the appearance of an inverted triangle, is formed by the fusion of the five sacral vertebrae (Fig. 5.22). The base of the sacrum articulates with vertebra LV, and its apex articulates with the coccyx. Each of the lateral surfaces of the bone bears a large L-shaped facet for articulation with the ilium of the pelvic bone. Posterior to the facet is a large roughened area for the attachment of ligaments that support the sacro-iliac joint. The superior surface of the sacrum is characterized by the superior aspect of the body of vertebra SI and is flanked on each side by an expanded wing-like transverse process termed the ala. The anterior edge of the vertebral body projects forward as the promontory. The anterior surface of the sacrum is concave; the posterior surface is convex. Because the transverse processes of adjacent sacral vertebrae fuse lateral to the position of the intervertebral foramina and lateral to the bifurcation of spinal nerves into posterior and	Anatomy_Gray. The sacrum, which has the appearance of an inverted triangle, is formed by the fusion of the five sacral vertebrae (Fig. 5.22). The base of the sacrum articulates with vertebra LV, and its apex articulates with the coccyx. Each of the lateral surfaces of the bone bears a large L-shaped facet for articulation with the ilium of the pelvic bone. Posterior to the facet is a large roughened area for the attachment of ligaments that support the sacro-iliac joint. The superior surface of the sacrum is characterized by the superior aspect of the body of vertebra SI and is flanked on each side by an expanded wing-like transverse process termed the ala. The anterior edge of the vertebral body projects forward as the promontory. The anterior surface of the sacrum is concave; the posterior surface is convex. Because the transverse processes of adjacent sacral vertebrae fuse lateral to the position of the intervertebral foramina and lateral to the bifurcation of spinal nerves into posterior and
Anatomy_Gray_1019	Anatomy_Gray	is convex. Because the transverse processes of adjacent sacral vertebrae fuse lateral to the position of the intervertebral foramina and lateral to the bifurcation of spinal nerves into posterior and anterior rami, the posterior and anterior rami of spinal nerves S1 to S4 emerge from the sacrum through separate foramina. There are four pairs of anterior sacral foramina on the anterior surface of the sacrum for anterior rami, and four pairs of posterior sacral foramina on the posterior surface for the posterior rami. The sacral canal is a continuation of the vertebral canal that terminates as the sacral hiatus.	Anatomy_Gray. is convex. Because the transverse processes of adjacent sacral vertebrae fuse lateral to the position of the intervertebral foramina and lateral to the bifurcation of spinal nerves into posterior and anterior rami, the posterior and anterior rami of spinal nerves S1 to S4 emerge from the sacrum through separate foramina. There are four pairs of anterior sacral foramina on the anterior surface of the sacrum for anterior rami, and four pairs of posterior sacral foramina on the posterior surface for the posterior rami. The sacral canal is a continuation of the vertebral canal that terminates as the sacral hiatus.
Anatomy_Gray_1020	Anatomy_Gray	The small terminal part of the vertebral column is the coccyx, which consists of four fused coccygeal vertebrae (Fig. 5.22) and, like the sacrum, has the shape of an inverted triangle. The base of the coccyx is directed superiorly. The superior surface bears a facet for articulation with the sacrum and two horns, or cornua, one on each side, that project upward to articulate or fuse with similar downward-projecting cornua from the sacrum. These processes are modified superior and inferior articular processes that are present on other vertebrae. Each lateral surface of the coccyx has a small rudimentary transverse process, extending from the first coccygeal vertebra. Vertebral arches are absent from coccygeal vertebrae; therefore no bony vertebral canal is present in the coccyx.	Anatomy_Gray. The small terminal part of the vertebral column is the coccyx, which consists of four fused coccygeal vertebrae (Fig. 5.22) and, like the sacrum, has the shape of an inverted triangle. The base of the coccyx is directed superiorly. The superior surface bears a facet for articulation with the sacrum and two horns, or cornua, one on each side, that project upward to articulate or fuse with similar downward-projecting cornua from the sacrum. These processes are modified superior and inferior articular processes that are present on other vertebrae. Each lateral surface of the coccyx has a small rudimentary transverse process, extending from the first coccygeal vertebra. Vertebral arches are absent from coccygeal vertebrae; therefore no bony vertebral canal is present in the coccyx.
Anatomy_Gray_1021	Anatomy_Gray	The sacrum articulates superiorly with the lumbar part of the vertebral column. The lumbosacral joints are formed between vertebra LV and the sacrum and consist of: the two zygapophysial joints, which occur between adjacent inferior and superior articular processes, and an intervertebral disc that joins the bodies of vertebrae LV and SI (Fig. 5.23A). These joints are similar to those between other vertebrae, with the exception that the sacrum is angled posteriorly on vertebra LV. As a result, the anterior part of the intervertebral disc between the two bones is thicker than the posterior part. The lumbosacral joints are reinforced by strong iliolumbar and lumbosacral ligaments that extend from the expanded transverse processes of vertebra LV to the ilium and the sacrum, respectively (Fig. 5.23B).	Anatomy_Gray. The sacrum articulates superiorly with the lumbar part of the vertebral column. The lumbosacral joints are formed between vertebra LV and the sacrum and consist of: the two zygapophysial joints, which occur between adjacent inferior and superior articular processes, and an intervertebral disc that joins the bodies of vertebrae LV and SI (Fig. 5.23A). These joints are similar to those between other vertebrae, with the exception that the sacrum is angled posteriorly on vertebra LV. As a result, the anterior part of the intervertebral disc between the two bones is thicker than the posterior part. The lumbosacral joints are reinforced by strong iliolumbar and lumbosacral ligaments that extend from the expanded transverse processes of vertebra LV to the ilium and the sacrum, respectively (Fig. 5.23B).
Anatomy_Gray_1022	Anatomy_Gray	The sacro-iliac joints transmit forces from the lower limbs to the vertebral column. They are synovial joints between the L-shaped articular facets on the lateral surfaces of the sacrum and similar facets on the iliac parts of the pelvic bones (Fig. 5.24A). The joint surfaces have an irregular contour and interlock to resist movement. The joints often become fibrous with age and may become completely ossified.	Anatomy_Gray. The sacro-iliac joints transmit forces from the lower limbs to the vertebral column. They are synovial joints between the L-shaped articular facets on the lateral surfaces of the sacrum and similar facets on the iliac parts of the pelvic bones (Fig. 5.24A). The joint surfaces have an irregular contour and interlock to resist movement. The joints often become fibrous with age and may become completely ossified.
Anatomy_Gray_1023	Anatomy_Gray	Each sacro-iliac joint is stabilized by three ligaments: the anterior sacro-iliac ligament, which is a thickening of the fibrous membrane of the joint capsule and runs anteriorly and inferiorly to the joint (Fig. 5.24B); the interosseous sacro-iliac ligament, which is the largest, strongest ligament of the three, and is positioned immediately posterosuperior to the joint and attaches to adjacent expansive roughened areas on the ilium and sacrum, thereby filling the gap between the two bones (Fig. 5.24A,C); and the posterior sacro-iliac ligament, which covers the interosseous sacro-iliac ligament (Fig. 5.24C).	Anatomy_Gray. Each sacro-iliac joint is stabilized by three ligaments: the anterior sacro-iliac ligament, which is a thickening of the fibrous membrane of the joint capsule and runs anteriorly and inferiorly to the joint (Fig. 5.24B); the interosseous sacro-iliac ligament, which is the largest, strongest ligament of the three, and is positioned immediately posterosuperior to the joint and attaches to adjacent expansive roughened areas on the ilium and sacrum, thereby filling the gap between the two bones (Fig. 5.24A,C); and the posterior sacro-iliac ligament, which covers the interosseous sacro-iliac ligament (Fig. 5.24C).
Anatomy_Gray_1024	Anatomy_Gray	The pubic symphysis lies anteriorly between the adjacent surfaces of the pubic bones (Fig. 5.25). Each of the joint’s surfaces is covered by hyaline cartilage and is linked across the midline to adjacent surfaces by fibrocartilage. The joint is surrounded by interwoven layers of collagen fibers and the two major ligaments associated with it are: the superior pubic ligament, located above the joint, and the inferior pubic ligament, located below it. In the anatomical position, the pelvis is oriented so that the front edge of the top of the pubic symphysis and the anterior superior iliac spines lie in the same vertical plane (Fig. 5.26). As a consequence, the pelvic inlet, which marks the entrance to the pelvic cavity, is tilted to face anteriorly, and the bodies of the pubic bones and the pubic arch are positioned in a nearly horizontal plane facing the ground.	Anatomy_Gray. The pubic symphysis lies anteriorly between the adjacent surfaces of the pubic bones (Fig. 5.25). Each of the joint’s surfaces is covered by hyaline cartilage and is linked across the midline to adjacent surfaces by fibrocartilage. The joint is surrounded by interwoven layers of collagen fibers and the two major ligaments associated with it are: the superior pubic ligament, located above the joint, and the inferior pubic ligament, located below it. In the anatomical position, the pelvis is oriented so that the front edge of the top of the pubic symphysis and the anterior superior iliac spines lie in the same vertical plane (Fig. 5.26). As a consequence, the pelvic inlet, which marks the entrance to the pelvic cavity, is tilted to face anteriorly, and the bodies of the pubic bones and the pubic arch are positioned in a nearly horizontal plane facing the ground.
Anatomy_Gray_1025	Anatomy_Gray	The pelvises of women and men differ in a number of ways, many of which have to do with the passing of a baby through a woman’s pelvic cavity during childbirth. The pelvic inlet in women is circular (Fig. 5.27A) compared with the heart-shaped pelvic inlet (Fig. 5.27B) in men. The more circular shape is partly caused by the less distinct promontory and broader alae in women. The angle formed by the two arms of the pubic arch is larger in women (80°–85°) than it is in men (50°–60°). The ischial spines generally do not project as far medially into the pelvic cavity in women as they do in men. The true pelvis is cylindrical and has an inlet, a wall, and an outlet. The inlet is open, whereas the pelvic floor closes the outlet and separates the pelvic cavity, above, from the perineum, below.	Anatomy_Gray. The pelvises of women and men differ in a number of ways, many of which have to do with the passing of a baby through a woman’s pelvic cavity during childbirth. The pelvic inlet in women is circular (Fig. 5.27A) compared with the heart-shaped pelvic inlet (Fig. 5.27B) in men. The more circular shape is partly caused by the less distinct promontory and broader alae in women. The angle formed by the two arms of the pubic arch is larger in women (80°–85°) than it is in men (50°–60°). The ischial spines generally do not project as far medially into the pelvic cavity in women as they do in men. The true pelvis is cylindrical and has an inlet, a wall, and an outlet. The inlet is open, whereas the pelvic floor closes the outlet and separates the pelvic cavity, above, from the perineum, below.
Anatomy_Gray_1026	Anatomy_Gray	The pelvic inlet is the circular opening between the abdominal cavity and the pelvic cavity through which structures traverse between the abdomen and pelvic cavity. It is completely surrounded by bones and joints (Fig. 5.28). The promontory of the sacrum protrudes into the inlet, forming its posterior margin in the midline. On either side of the promontory, the margin is formed by the alae of the sacrum. The margin of the pelvic inlet then crosses the sacro-iliac joint and continues along the linea terminalis (i.e., the arcuate line, the pecten pubis or pectineal line, and the pubic crest) to the pubic symphysis. The walls of the pelvic cavity consist of the sacrum, the coccyx, the pelvic bones inferior to the linea terminalis, two ligaments, and two muscles. Ligaments of the pelvic wall	Anatomy_Gray. The pelvic inlet is the circular opening between the abdominal cavity and the pelvic cavity through which structures traverse between the abdomen and pelvic cavity. It is completely surrounded by bones and joints (Fig. 5.28). The promontory of the sacrum protrudes into the inlet, forming its posterior margin in the midline. On either side of the promontory, the margin is formed by the alae of the sacrum. The margin of the pelvic inlet then crosses the sacro-iliac joint and continues along the linea terminalis (i.e., the arcuate line, the pecten pubis or pectineal line, and the pubic crest) to the pubic symphysis. The walls of the pelvic cavity consist of the sacrum, the coccyx, the pelvic bones inferior to the linea terminalis, two ligaments, and two muscles. Ligaments of the pelvic wall
Anatomy_Gray_1027	Anatomy_Gray	The walls of the pelvic cavity consist of the sacrum, the coccyx, the pelvic bones inferior to the linea terminalis, two ligaments, and two muscles. Ligaments of the pelvic wall The sacrospinous and sacrotuberous ligaments (Fig. 5.29A) are major components of the lateral pelvic walls that help define the apertures between the pelvic cavity and adjacent regions through which structures pass. The smaller of the two, the sacrospinous ligament, is triangular, with its apex attached to the ischial spine and its base attached to the related margins of the sacrum and the coccyx. The sacrotuberous ligament is also triangular and is superficial to the sacrospinous ligament. Its base has a broad attachment that extends from the posterior superior iliac spine of the pelvic bone, along the dorsal aspect and the lateral margin of the sacrum, and onto the dorsolateral surface of the coccyx. Laterally, the apex of the ligament is attached to the medial margin of the ischial tuberosity.	Anatomy_Gray. The walls of the pelvic cavity consist of the sacrum, the coccyx, the pelvic bones inferior to the linea terminalis, two ligaments, and two muscles. Ligaments of the pelvic wall The sacrospinous and sacrotuberous ligaments (Fig. 5.29A) are major components of the lateral pelvic walls that help define the apertures between the pelvic cavity and adjacent regions through which structures pass. The smaller of the two, the sacrospinous ligament, is triangular, with its apex attached to the ischial spine and its base attached to the related margins of the sacrum and the coccyx. The sacrotuberous ligament is also triangular and is superficial to the sacrospinous ligament. Its base has a broad attachment that extends from the posterior superior iliac spine of the pelvic bone, along the dorsal aspect and the lateral margin of the sacrum, and onto the dorsolateral surface of the coccyx. Laterally, the apex of the ligament is attached to the medial margin of the ischial tuberosity.
Anatomy_Gray_1028	Anatomy_Gray	These ligaments stabilize the sacrum on the pelvic bones by resisting the upward tilting of the inferior aspect of the sacrum (Fig. 5.29B). They also convert the greater and lesser sciatic notches of the pelvic bone into foramina (Fig. 5.29A,B). The greater sciatic foramen lies superior to the sacrospinous ligament and the ischial spine. The lesser sciatic foramen lies inferior to the ischial spine and sacrospinous ligament between the sacrospinous and sacrotuberous ligaments. Muscles of the pelvic wall Two muscles, the obturator internus and the piriformis, contribute to the lateral walls of the pelvic cavity. These muscles originate in the pelvic cavity but attach peripherally to the femur. The obturator internus is a flat, fan-shaped muscle that originates from the deep surface of the obturator membrane and from associated regions of the pelvic bone that surround the obturator foramen (Fig. 5.30 and Table 5.1).	Anatomy_Gray. These ligaments stabilize the sacrum on the pelvic bones by resisting the upward tilting of the inferior aspect of the sacrum (Fig. 5.29B). They also convert the greater and lesser sciatic notches of the pelvic bone into foramina (Fig. 5.29A,B). The greater sciatic foramen lies superior to the sacrospinous ligament and the ischial spine. The lesser sciatic foramen lies inferior to the ischial spine and sacrospinous ligament between the sacrospinous and sacrotuberous ligaments. Muscles of the pelvic wall Two muscles, the obturator internus and the piriformis, contribute to the lateral walls of the pelvic cavity. These muscles originate in the pelvic cavity but attach peripherally to the femur. The obturator internus is a flat, fan-shaped muscle that originates from the deep surface of the obturator membrane and from associated regions of the pelvic bone that surround the obturator foramen (Fig. 5.30 and Table 5.1).
Anatomy_Gray_1029	Anatomy_Gray	The muscle fibers of the obturator internus converge to form a tendon that leaves the pelvic cavity through the lesser sciatic foramen, makes a 90° bend around the ischium between the ischial spine and ischial tuberosity, and then passes posterior to the hip joint to insert on the greater trochanter of the femur. The obturator internus forms a large part of the anterolateral wall of the pelvic cavity. The piriformis is triangular and originates in the bridges of bone between the four anterior sacral foramina. It passes laterally through the greater sciatic foramen, crosses the posterosuperior aspect of the hip joint, and inserts on the greater trochanter of the femur above the insertion of the obturator internus muscle (Fig. 5.30 and Table 5.1).	Anatomy_Gray. The muscle fibers of the obturator internus converge to form a tendon that leaves the pelvic cavity through the lesser sciatic foramen, makes a 90° bend around the ischium between the ischial spine and ischial tuberosity, and then passes posterior to the hip joint to insert on the greater trochanter of the femur. The obturator internus forms a large part of the anterolateral wall of the pelvic cavity. The piriformis is triangular and originates in the bridges of bone between the four anterior sacral foramina. It passes laterally through the greater sciatic foramen, crosses the posterosuperior aspect of the hip joint, and inserts on the greater trochanter of the femur above the insertion of the obturator internus muscle (Fig. 5.30 and Table 5.1).
Anatomy_Gray_1030	Anatomy_Gray	A large part of the posterolateral wall of the pelvic cavity is formed by the piriformis. In addition, this muscle separates the greater sciatic foramen into two regions, one above the muscle and one below. Vessels and nerves coursing between the pelvic cavity and the gluteal region pass through these two regions. Apertures in the pelvic wall Each lateral pelvic wall has three major apertures through which structures pass between the pelvic cavity and other regions: the obturator canal, the greater sciatic foramen, and the lesser sciatic foramen. At the top of the obturator foramen is the obturator canal, which is bordered by the obturator membrane, the associated obturator muscles, and the superior pubic ramus (Fig. 5.31). The obturator nerve and vessels pass from the pelvic cavity to the thigh through this canal.	Anatomy_Gray. A large part of the posterolateral wall of the pelvic cavity is formed by the piriformis. In addition, this muscle separates the greater sciatic foramen into two regions, one above the muscle and one below. Vessels and nerves coursing between the pelvic cavity and the gluteal region pass through these two regions. Apertures in the pelvic wall Each lateral pelvic wall has three major apertures through which structures pass between the pelvic cavity and other regions: the obturator canal, the greater sciatic foramen, and the lesser sciatic foramen. At the top of the obturator foramen is the obturator canal, which is bordered by the obturator membrane, the associated obturator muscles, and the superior pubic ramus (Fig. 5.31). The obturator nerve and vessels pass from the pelvic cavity to the thigh through this canal.
Anatomy_Gray_1031	Anatomy_Gray	The greater sciatic foramen is a major route of communication between the pelvic cavity and the lower limb (Fig. 5.31). It is formed by the greater sciatic notch in the pelvic bone, the sacrotuberous and the sacrospinous ligaments, and the spine of the ischium. The piriformis muscle passes through the greater sciatic foramen, dividing it into two parts. The superior gluteal nerves and vessels pass through the foramen above the piriformis. Passing through the foramen below the piriformis are the inferior gluteal nerves and vessels, the sciatic nerve, the pudendal nerve, the internal pudendal vessels, the posterior femoral cutaneous nerves, and the nerves to the obturator internus and quadratus femoris muscles. The lesser sciatic foramen is formed by the lesser sciatic notch of the pelvic bone, the ischial spine, the sacrospinous ligament, and the sacrotuberous ligament (Fig. 5.31).	Anatomy_Gray. The greater sciatic foramen is a major route of communication between the pelvic cavity and the lower limb (Fig. 5.31). It is formed by the greater sciatic notch in the pelvic bone, the sacrotuberous and the sacrospinous ligaments, and the spine of the ischium. The piriformis muscle passes through the greater sciatic foramen, dividing it into two parts. The superior gluteal nerves and vessels pass through the foramen above the piriformis. Passing through the foramen below the piriformis are the inferior gluteal nerves and vessels, the sciatic nerve, the pudendal nerve, the internal pudendal vessels, the posterior femoral cutaneous nerves, and the nerves to the obturator internus and quadratus femoris muscles. The lesser sciatic foramen is formed by the lesser sciatic notch of the pelvic bone, the ischial spine, the sacrospinous ligament, and the sacrotuberous ligament (Fig. 5.31).
Anatomy_Gray_1032	Anatomy_Gray	The lesser sciatic foramen is formed by the lesser sciatic notch of the pelvic bone, the ischial spine, the sacrospinous ligament, and the sacrotuberous ligament (Fig. 5.31). The tendon of the obturator internus muscle passes through this foramen to enter the gluteal region of the lower limb. Because the lesser sciatic foramen is positioned below the attachment of the pelvic floor, it acts as a route of communication between the perineum and the gluteal region. The pudendal nerve and internal pudendal vessels pass between the pelvic cavity (above the pelvic floor) and the perineum (below the pelvic floor), by first passing out of the pelvic cavity through the greater sciatic foramen and then looping around the ischial spine and sacrospinous ligament to pass through the lesser sciatic foramen to enter the perineum. The nerve to obturator internus follows a similar course.	Anatomy_Gray. The lesser sciatic foramen is formed by the lesser sciatic notch of the pelvic bone, the ischial spine, the sacrospinous ligament, and the sacrotuberous ligament (Fig. 5.31). The tendon of the obturator internus muscle passes through this foramen to enter the gluteal region of the lower limb. Because the lesser sciatic foramen is positioned below the attachment of the pelvic floor, it acts as a route of communication between the perineum and the gluteal region. The pudendal nerve and internal pudendal vessels pass between the pelvic cavity (above the pelvic floor) and the perineum (below the pelvic floor), by first passing out of the pelvic cavity through the greater sciatic foramen and then looping around the ischial spine and sacrospinous ligament to pass through the lesser sciatic foramen to enter the perineum. The nerve to obturator internus follows a similar course.
Anatomy_Gray_1033	Anatomy_Gray	The pelvic outlet is diamond shaped, with the anterior part of the diamond defined predominantly by bone and the posterior part mainly by ligaments (Fig. 5.32). In the midline anteriorly, the boundary of the pelvic outlet is the pubic symphysis. Extending laterally and posteriorly, the boundary on each side is the inferior border of the body of the pubis, the inferior ramus of the pubis, the ramus of the ischium, and the ischial tuberosity. Together, the elements on both sides form the pubic arch. From the ischial tuberosities, the boundaries continue posteriorly and medially along the sacrotuberous ligament on both sides to the coccyx. Terminal parts of the urinary and gastrointestinal tracts and the vagina pass through the pelvic outlet. The area enclosed by the boundaries of the pelvic outlet and below the pelvic floor is the perineum.	Anatomy_Gray. The pelvic outlet is diamond shaped, with the anterior part of the diamond defined predominantly by bone and the posterior part mainly by ligaments (Fig. 5.32). In the midline anteriorly, the boundary of the pelvic outlet is the pubic symphysis. Extending laterally and posteriorly, the boundary on each side is the inferior border of the body of the pubis, the inferior ramus of the pubis, the ramus of the ischium, and the ischial tuberosity. Together, the elements on both sides form the pubic arch. From the ischial tuberosities, the boundaries continue posteriorly and medially along the sacrotuberous ligament on both sides to the coccyx. Terminal parts of the urinary and gastrointestinal tracts and the vagina pass through the pelvic outlet. The area enclosed by the boundaries of the pelvic outlet and below the pelvic floor is the perineum.
Anatomy_Gray_1034	Anatomy_Gray	The area enclosed by the boundaries of the pelvic outlet and below the pelvic floor is the perineum. The pelvic floor is formed by the pelvic diaphragm and, in the anterior midline, the perineal membrane and the muscles in the deep perineal pouch. The pelvic diaphragm is formed by the levator ani and the coccygeus muscles from both sides. The pelvic floor separates the pelvic cavity, above, from the perineum, below. The pelvic diaphragm The pelvic diaphragm is the muscular part of the pelvic floor. Shaped like a bowl or funnel and attached superiorly to the pelvic walls, it consists of the levator ani and the coccygeus muscles (Fig. 5.34 and Table 5.2).	Anatomy_Gray. The area enclosed by the boundaries of the pelvic outlet and below the pelvic floor is the perineum. The pelvic floor is formed by the pelvic diaphragm and, in the anterior midline, the perineal membrane and the muscles in the deep perineal pouch. The pelvic diaphragm is formed by the levator ani and the coccygeus muscles from both sides. The pelvic floor separates the pelvic cavity, above, from the perineum, below. The pelvic diaphragm The pelvic diaphragm is the muscular part of the pelvic floor. Shaped like a bowl or funnel and attached superiorly to the pelvic walls, it consists of the levator ani and the coccygeus muscles (Fig. 5.34 and Table 5.2).
Anatomy_Gray_1035	Anatomy_Gray	The pelvic diaphragm’s circular line of attachment to the cylindrical pelvic wall passes, on each side, between the greater sciatic foramen and the lesser sciatic foramen. Thus: the greater sciatic foramen is situated above the level of the pelvic floor and is a route of communication between the pelvic cavity and the gluteal region of the lower limb; and the lesser sciatic foramen is situated below the pelvic floor, providing a route of communication between the gluteal region of the lower limb and the perineum. The two levator ani muscles originate from each side of the pelvic wall, course medially and inferiorly, and join together in the midline. The attachment to the pelvic wall follows the circular contour of the wall and includes: the posterior aspect of the body of the pubic bone, a linear thickening called the tendinous arch, in the fascia covering the obturator internus muscle, and the spine of the ischium.	Anatomy_Gray. The pelvic diaphragm’s circular line of attachment to the cylindrical pelvic wall passes, on each side, between the greater sciatic foramen and the lesser sciatic foramen. Thus: the greater sciatic foramen is situated above the level of the pelvic floor and is a route of communication between the pelvic cavity and the gluteal region of the lower limb; and the lesser sciatic foramen is situated below the pelvic floor, providing a route of communication between the gluteal region of the lower limb and the perineum. The two levator ani muscles originate from each side of the pelvic wall, course medially and inferiorly, and join together in the midline. The attachment to the pelvic wall follows the circular contour of the wall and includes: the posterior aspect of the body of the pubic bone, a linear thickening called the tendinous arch, in the fascia covering the obturator internus muscle, and the spine of the ischium.
Anatomy_Gray_1036	Anatomy_Gray	At the midline, the muscles blend together posterior to the vagina in women and around the anal aperture in both sexes. Posterior to the anal aperture, the muscles come together as a ligament or raphe called the anococcygeal ligament (anococcygeal body) and attaches to the coccyx. Anteriorly, the muscles are separated by a U-shaped defect or gap termed the urogenital hiatus. The margins of this hiatus merge with the walls of the associated viscera and with muscles in the deep perineal pouch below. The hiatus allows the urethra (in both men and women), and the vagina (in women), to pass through the pelvic diaphragm (Fig. 5.34). The levator ani muscles are divided into at least three collections of muscle fibers, based on site of origin and relationship to viscera in the midline: the pubococcygeus, the puborectalis, and the iliococcygeus muscles.	Anatomy_Gray. At the midline, the muscles blend together posterior to the vagina in women and around the anal aperture in both sexes. Posterior to the anal aperture, the muscles come together as a ligament or raphe called the anococcygeal ligament (anococcygeal body) and attaches to the coccyx. Anteriorly, the muscles are separated by a U-shaped defect or gap termed the urogenital hiatus. The margins of this hiatus merge with the walls of the associated viscera and with muscles in the deep perineal pouch below. The hiatus allows the urethra (in both men and women), and the vagina (in women), to pass through the pelvic diaphragm (Fig. 5.34). The levator ani muscles are divided into at least three collections of muscle fibers, based on site of origin and relationship to viscera in the midline: the pubococcygeus, the puborectalis, and the iliococcygeus muscles.
Anatomy_Gray_1037	Anatomy_Gray	The pubococcygeus originates from the body of the pubis and courses posteriorly to attach along the midline as far back as the coccyx. This part of the muscle is further subdivided on the basis of association with structures in the midline into the puboprostaticus (levator prostatae), the pubovaginalis, and the puboanalis muscles. A second major collection of muscle fibers, the puborectalis portion of the levator ani muscles, originates, in association with the pubococcygeus muscle, from the pubis and passes inferiorly on each side to form a sling around the terminal part of the gastrointestinal tract. This muscular sling maintains an angle or flexure, called the perineal flexure, at the anorectal junction. This angle functions as part of the mechanism that keeps the end of the gastrointestinal system closed.	Anatomy_Gray. The pubococcygeus originates from the body of the pubis and courses posteriorly to attach along the midline as far back as the coccyx. This part of the muscle is further subdivided on the basis of association with structures in the midline into the puboprostaticus (levator prostatae), the pubovaginalis, and the puboanalis muscles. A second major collection of muscle fibers, the puborectalis portion of the levator ani muscles, originates, in association with the pubococcygeus muscle, from the pubis and passes inferiorly on each side to form a sling around the terminal part of the gastrointestinal tract. This muscular sling maintains an angle or flexure, called the perineal flexure, at the anorectal junction. This angle functions as part of the mechanism that keeps the end of the gastrointestinal system closed.
Anatomy_Gray_1038	Anatomy_Gray	The final part of the levator ani muscle is the iliococcygeus. This part of the muscle originates from the fascia that covers the obturator internus muscle. It joins the same muscle on the other side in the midline to form a ligament or raphe that extends from the anal aperture to the coccyx. The levator ani muscles help support the pelvic viscera and maintain closure of the rectum and vagina. They are innervated directly by branches from the anterior ramus of S4 and by branches of the pudendal nerve (S2 to S4). The two coccygeus muscles, one on each side, are triangular and overlie the sacrospinous ligaments; together they complete the posterior part of the pelvic diaphragm (Fig. 5.34 and Table 5.2). They are attached, by their apices, to the tips of the ischial spines and, by their bases, to the lateral margins of the coccyx and adjacent margins of the sacrum.	Anatomy_Gray. The final part of the levator ani muscle is the iliococcygeus. This part of the muscle originates from the fascia that covers the obturator internus muscle. It joins the same muscle on the other side in the midline to form a ligament or raphe that extends from the anal aperture to the coccyx. The levator ani muscles help support the pelvic viscera and maintain closure of the rectum and vagina. They are innervated directly by branches from the anterior ramus of S4 and by branches of the pudendal nerve (S2 to S4). The two coccygeus muscles, one on each side, are triangular and overlie the sacrospinous ligaments; together they complete the posterior part of the pelvic diaphragm (Fig. 5.34 and Table 5.2). They are attached, by their apices, to the tips of the ischial spines and, by their bases, to the lateral margins of the coccyx and adjacent margins of the sacrum.
Anatomy_Gray_1039	Anatomy_Gray	The coccygeus muscles are innervated by branches from the anterior rami of S3 and S4 and participate in supporting the posterior aspect of the pelvic floor. The perineal membrane and deep The perineal membrane is a thick fascial, triangular structure attached to the bony framework of the pubic arch (Fig. 5.36A). It is oriented in the horizontal plane and has a free posterior margin. Anteriorly, there is a small gap (blue arrow in Fig. 5.36A) between the membrane and the inferior pubic ligament (a ligament associated with the pubic symphysis). The perineal membrane is related above to a thin space called the deep perineal pouch (deep perineal space) (Fig. 5.36B), which contains a layer of skeletal muscle and various neurovascular elements.	Anatomy_Gray. The coccygeus muscles are innervated by branches from the anterior rami of S3 and S4 and participate in supporting the posterior aspect of the pelvic floor. The perineal membrane and deep The perineal membrane is a thick fascial, triangular structure attached to the bony framework of the pubic arch (Fig. 5.36A). It is oriented in the horizontal plane and has a free posterior margin. Anteriorly, there is a small gap (blue arrow in Fig. 5.36A) between the membrane and the inferior pubic ligament (a ligament associated with the pubic symphysis). The perineal membrane is related above to a thin space called the deep perineal pouch (deep perineal space) (Fig. 5.36B), which contains a layer of skeletal muscle and various neurovascular elements.