Atlas ( anatomy ) - wikipedia Atlas ( anatomy ) See also : Atlas ( disambiguation ) Atlas ( anatomy ) Position of the atlas ( shown in red ) Details Identifiers Latin Atlas, vertebra cervicalis I Dorlands / Elsevier a_70 / 12167134 TA A02. 2.02. 101 FMA 12519 Anatomical terms of bone ( edit on Wikidata ) In anatomy, the atlas ( C1 ) is the most superior ( first ) cervical vertebra of the spine. It is named for the Atlas of Greek mythology, because it supports the globe of the head. The atlas is the topmost vertebra and with the axis forms the joint connecting the skull and spine. The atlas and axis are specialized to allow a greater range of motion than normal vertebrae. They are responsible for the nodding and rotation movements of the head. The atlanto - occipital joint allows the head to nod up and down on the vertebral column. The dens acts as a pivot that allows the atlas and attached head to rotate on the axis, side to side. The atlas 's chief peculiarity is that it has no body. It is ring - like and consists of an anterior and a posterior arch and two lateral masses. The atlas and axis are important neurologically because the brain stem extends down to the axis. Contents 1 Structure 1.1 Anterior arch 1.2 Posterior arch 1.3 Lateral masses 1.4 Vertebral foramen 1.5 Transverse processes 1.6 Development 2 Function 2.1 Muscular attachments 2.1. 1 Transverse processes 2.1. 2 Posterior tubercle 2.1. 3 Anterior arch 3 Clinical significance 4 Additional images 5 See also 6 References 7 External links Structure Structure of the atlas, the first cervical vertebra Anterior arch The anterior arch forms about one - fifth of the ring : its anterior surface is convex, and presents at its center the anterior tubercle for the attachment of the Longus colli muscles and the anterior longitudinal ligament ; posteriorly it is concave, and marked by a smooth, oval or circular facet ( fovea dentis ), for articulation with the odontoid process ( dens ) of the axis. The upper and lower borders respectively give attachment to the anterior atlantooccipital membrane and the anterior atlantoaxial ligament ; the former connects it with the occipital bone above, and the latter with the axis below. Posterior arch Median sagittal section through the occipital bone and first three cervical vertebræ, showing ligamentous attachments The posterior arch forms about two - fifths of the circumference of the ring : it ends behind in the posterior tubercle, which is the rudiment of a spinous process and gives origin to the Recti capitis posteriores minores and the ligamentum nuchae. The diminutive size of this process prevents any interference with the movements between the atlas and the skull. The posterior part of the arch presents above and behind a rounded edge for the attachment of the posterior atlantooccipital membrane, while immediately behind each superior articular process is the superior vertebral notch ( sulcus arteriae vertebralis ). This is a groove that is sometimes converted into a foramen by ossification of the posterior atlantooccipital membrane to create a delicate bony spiculum which arches backward from the posterior end of the superior articular process. This anatomical variant is known as an arcuate foramen. This groove transmits the vertebral artery, which, after ascending through the foramen in the transverse process, winds around the lateral mass in a direction backward and medially to enter the vertebrobasilar circulation through the foramen magnum ; it also transmits the suboccipital nerve ( first spinal nerve ) On the under surface of the posterior arch, behind the inferior articular facets, are two shallow grooves, the inferior vertebral notches. The lower border gives attachment to the posterior atlantoaxial ligament, which connects it with the axis. Lateral masses The lateral masses are the most bulky and solid parts of the atlas, in order to support the weight of the head. Each carries two articular facets, a superior and an inferior. The superior facets are of large size, oval, concave, and approach each other in front, but diverge behind : they are directed upward, medially, and a little backward, each forming a cup for the corresponding condyle of the occipital bone, and are admirably adapted to the nodding movements of the head. Not infrequently they are partially subdivided by indentations which encroach upon their margins. The inferior articular facets are circular in form, flattened or slightly convex and directed downward and medially, articulating with the axis, and permitting the rotatory movements of the head. Vertebral foramen Just below the medial margin of each superior facet is a small tubercle, for the attachment of the transverse atlantal ligament which stretches across the ring of the atlas and divides the vertebral foramen into two unequal parts : the anterior or smaller receiving the odontoid process of the axis the posterior transmitting the spinal cord ( medulla spinalis ) and its membranes This part of the vertebral canal is of considerable size, much greater than is required for the accommodation of the spinal cord. Transverse processes The transverse processes are large ; they project laterally and downward from the lateral masses, and serve for the attachment of muscles which assist in rotating the head. They are long, and their anterior and posterior tubercles are fused into one mass ; the foramen transversarium is directed from below, upward and backward. Development The atlas ossifies from three centers The atlas is usually ossified from three centers. Of these, one appears in each lateral mass about the seventh week of fetal life, and extends backward ; at birth, these portions of bone are separated from one another behind by a narrow interval filled with cartilage. Between the third and fourth years they unite either directly or through the medium of a separate center developed in the cartilage. At birth, the anterior arch consists of cartilage ; in this a separate center appears about the end of the first year after birth, and joins the lateral masses from the sixth to the eighth year. The lines of union extend across the anterior portions of the superior articular facets. Occasionally there is no separate center, the anterior arch being formed by the forward extension and ultimate junction of the two lateral masses ; sometimes this arch is ossified from two centers, one on either side of the middle line. Function Muscular attachments Transverse processes Upper surface : rectus capitis anterior -- occipital bone ( inferior surface of the base ) rectus capitis lateralis -- occipital bone ( beneath the jugular process ) obliquus capitis superior -- occipital bone ( between the superior and inferior nuchal lines ) Interior and dorsal part : obliquus capitis inferior -- spinous process of the axis Lower surface : splenius cervicis ( part ) -- spinous processes of T02 -- T05 levator scapulae ( part ) -- superior part of medial border of the scapula intertransversarius posterior cervicis -- transverse process of the axis ( posterior tubercle ) intertransversarius anterior cervicis -- transverse process of the axis ( anterior turbercle ) Posterior tubercle Upper surface : rectus capitis posterior minor -- occipital bone ( medial part of the interior nuchal line, and the surface between it and the foramen magnum ) Lower surface : interspinalis cervicis -- spinous process of the axis Anterior arch longus colli ( superior oblique ) -- transverse processes of C03 -- C05. Clinical significance This section needs expansion. You can help by adding to it. ( April 2014 ) A break in the first vertebra is referred to as a Jefferson fracture. Additional images Shape and position of atlas ( shown in red ), from above. The skull is shown in semi-transparent. Atlas from above Posterior atlantoöccipital membrane and atlantoaxial ligament ( atlas visible at center ) Atlas from above Atlas from above Atlas, inferior surface See also This article uses anatomical terminology ; for an overview, see Anatomical terminology. Occipital condyle References This article incorporates text in the public domain from the 20th edition of Gray 's Anatomy ( 1918 ) Jump up ^ the medical dictionary ; the free dictionary. Jump up ^ Gray 's Anatomy, pp. 36 -- 37 ( 10 / 27 / 11 ) External links Wikimedia Commons has media related to Atlas ( anatomy ). Netter, Frank. Atlas of Human Anatomy, `` High Cervical Spine : C1 -- C2 '' Bones of torso Vertebrae General structure Body Arch pedicle lamina notch Vertebral foramen Intervertebral foramen Processes transverse articular spinous Spinal canal Cervical vertebrae Uncinate process of vertebra Transverse foramen Anterior tubercle Carotid tubercle Posterior tubercle Atlas lateral mass anterior arch posterior arch Axis dens Vertebra prominens Thoracic vertebrae Costal facets superior inferior transverse Uncinate process of vertebra Lumbar vertebrae Processes accessory mammillary Sacrum Base sacral promontory Ala of sacrum Lateral surface sacral tuberosity Pelvic surface anterior sacral foramina Dorsal surface posterior sacral foramina Median sacral crest Medial sacral crest Lateral sacral crest Sacral canal sacral hiatus Coccyx Coccygeal cornu Thorax Rib cage Ribs true ribs false ribs floating ribs Parts angle tubercle costal groove neck head Sternum Suprasternal notch Manubrium Sternal angle Body of sternum Xiphisternal joint Xiphoid process Thoracic cage Thoracic inlet Thoracic outlet Intercostal space Costal margin Infrasternal angle Retrieved from `` https://en.wikipedia.org/w/index.php?title=Atlas_(anatomy)&oldid=811297689 '' Categories : Wikipedia articles incorporating text from the 20th edition of Gray 's Anatomy ( 1918 ) Bones of the thorax Hidden categories : Medicine infobox template using GraySubject or GrayPage Medicine infobox template using Dorlands parameter All articles with unsourced statements Articles with unsourced statements from November 2015 Articles to be expanded from April 2014 All articles to be expanded Articles using small message boxes Talk Contents About Wikipedia Azərbaycanca Башҡортса Български Català Čeština Dansk Deutsch Español Esperanto Euskara فارسی Français Gaeilge Galego Ido Italiano עברית Қазақша Latina Lietuvių Македонски Bahasa Melayu Nederlands नेपाल भाषा 日本 語 Norsk nynorsk Oʻzbekcha / ўзбекча Polski Português Русский Simple English Slovenčina Српски / srpski Suomi Svenska தமிழ் Türkçe Українська Edit links This page was last edited on 20 November 2017, at 19 : 09. 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Question: what is the most posterior structure of the atlas c1 vertebra
Answer: posterior arch