04-00
Muscular Tissue04-00 Muscular tissue

04 Muscular Tissue
Menu 1/2
04-00.

Muscular tissue04-14.

04-001. Skeletal muscle

04-15.

Motor nerve endings 3. Monkey tongue， silver impregnation， x400.

04-01.

Skeletal muscles， longitudinal section 1. Human tongue， H-E stain， x 160.

04-16.

Capillaries in the skeletal muscle fibers. Cat， infusion of India ink， x 100.

04-02.

Skeletal muscles， longitudinal section 2. Monkey， H-E stain， x 250.

04-17.

Muscle-tendon junction 1. Monkey， H-E stain， x 160.

04-03.

Skeletal muscles， longitudinal section 3. Human tongue， H-E stain， x 400.

04-18.

Muscle-tendon junction 2. Monkey， H-E stain， x 160.

04-04.

Skeletal muscles， longitudinal section 4. Rat， Heidenhain’s iron-hematoxylin stain，
x 500.

04-002. Cardiac muscle
04-19.

Cardiac muscles， longitudinal section 1. Human， H-E stain， x 250.

04-05.

Scheme showing ultrastructure of a myofilament

04-20.

Cardiac muscles， longitudinal section 2. Human， H-E stain， x 250.

04-06.

Skeletal muscle fibers， transverse section 1. Human， H-E stain， x 500.

04-21.

Cardiac muscles， longitudinal section 3. Human， M-G stain， x 250.

04-07.

Skeletal muscle fibers， longitudinal section. Endomysium 1. Human， Silver
impregnation and Kernechtrot stain， x 250.

04-22.

Cardiac muscles， transverse section 1. Human， H-E stain， x 160.

04-08.

Skeletal muscle fibers， longitudinal section. Endomysium 2. Human， Silver
impregnation and Kernechtrot stain， x 250.

04-23.

Cardiac muscles， transverse section 2. Human， M-G stain， x 250.

04-24.

Cardiac muscles， specialized conducting fibers 1. Human， M-G stain， x 64.
Purkinje fibers. Bovine， H-E stain， x 64.

Motor nerve endings 2. Monkey tongue， silver impregnation， x160.

04-09.

Skeletal muscle fibers， transverse section 2. Human， Silver impregnation and
Kernechtrot stain， x 400.

04-25.
04-26.

Cardiac muscle fibers，specialized conducting fibers. Human， M-G stain， x 160.

04-10.

Muscle spindle 1. Human， H-E stain， x 64.

04-27.

Cardiac muscle fibers， specialized conducting fibers. Human， H-E stain， x 250.

04-11.

Muscle spindle 2. Human， H-E stain， x 160.

04-12.

Muscle spindle 3. Rat， monoclonal antibody reaction using synaptophisin， x 130.

04-13.

Motor nerve endings 1. Monkey tongue， silver impregnation， x 64.

04 Muscular Tissue
Menu 1/2
04-28.

Junction between specialized conducting fibers and normal cardiac fibers. Human，
H-E stain. X 160.

04-003. Smooth Muscles
04-29.

Smooth muscle fibers， longitudinal section. Human， H-E stain. X 160.

04-30.

Smooth muscle fibers， longitudinal section. Monkey， H-E stain. X 250.

04-31.

Smooth muscle fibers， longitudinal section. Human， silver impregnation and
Kernechtrot stain. X 250.

04-32.

Smooth muscle fibers， transverse section. Human， H-E stain. X 160.

04-33.

Smooth muscle fibers， transverse section. Human， H-E stain. X 400.

04-34.

Smooth muscle fibers， transverse section. Human， silver impregnation and
Kernechtrot stain. X 250.

04-001
Skeletal Muscle
04-001 Skeletal muscle

04-01 Skeletal muscles， longitudinal section 1. Human tongue， H-E stain， x 160.

04-02 Skeletal muscles， longitudinal section 2. Monkey， H-E stain， x 250.

04-03 Skeletal muscles， longitudinal section 3. Human tongue， H-E stain， x 400.

04-04 Skeletal muscles， longitudinal section 4. Rat，
Heidenhain’s iron-hematoxylin stain， x 500.

Z lineZ lineSarcomere
A bandI bandH bandI bandMyofibrilThin
filament
Thick filament

M line04-05 Scheme showing ultrastructure of a myofilament.

04-06 Skeletal muscle fibers， transverse section 1. Human， H-E stain， x 500.

04-07 Skeletal muscle fibers， longitudinal section. Endomysium 1. Human，Silver impregnation and Kernechtrot stain， x 250.

04-08 Skeletal muscle fibers， longitudinal section. Endomysium 2. Human，Silver impregnation and Kernechtrot stain， x 250.

04-09 Skeletal muscle fibers， transverse section 2. Human， Silver impregnation and Kernechtrot stain， x 400.

04-10 Muscle spindle 1. Human， H-E stain， x 64.

04-11 Muscle spindle 2. Human， H-E stain， x 160.

04-12 Muscle spindle 3. Rat， monoclonal antibody reaction using synaptophisin， x 130.

04-13 Motor nerve endings 1. Monkey tongue， silver impregnation， x 64.

04-14 Motor nerve endings 2. Monkey tongue， silver impregnation， x160.

04-15 Motor nerve endings 3. Monkey tongue， silver impregnation， x400.

04-16 Capillaries in the skeletal muscle fibers. Cat， infusion of India ink， x 100.

04-17 Muscle-tendon junction 1. Monkey， H-E stain， x 160.

04-18 Muscle-tendon junction 2. Monkey， H-E stain， x 160.

04-002
Cardiac Muscle
04-002 Cardiac muscle

04-19 Cardiac muscles， longitudinal section 1. Human， H-E stain， x 250.

04-20 Cardiac muscles， longitudinal section 2. Human， H-E stain， x 250.

04-21 Cardiac muscles， longitudinal section 3. Human， M-G stain， x 250.

04-22 Cardiac muscles， transverse section 1. Human， H-E stain， x 160.

04-23 Cardiac muscles， transverse section 2. Human， M-G stain， x 250.

04-24 Cardiac muscles， specialized conducting
fibers 1. Human， M-G stain， x 64.

04-25 Purkinje fibers. Bovine， H-E stain， x 64.

04-26 Cardiac muscle fibers，specialized conducting fibers. Human， M-G stain， x 160.

04-27 Cardiac muscle fibers， specialized conducting fibers. Human， H-E stain， x 250.

04-28 Junction between specialized conducting fibers and normal cardiac fibers. Human，
H-E stain. X 160.

04-003
Smooth Muscle
04-003 Smooth Muscles

04-29 Smooth muscle fibers， longitudinal section. Human， H-E stain. X 160.

04-30 Smooth muscle fibers， longitudinal section. Monkey， H-E stain. X 250.

04-31 Smooth muscle fibers， longitudinal section. Human， silver impregnation and
Kernechtrot stain. X 250.

04-32 Smooth muscle fibers， transverse section. Human， H-E stain. X 160.

04-33 Smooth muscle fibers， transverse section. Human， H-E stain. X 400.

04-34 Smooth muscle fibers， transverse section. Human， silver impregnation and
Kernechtrot stain. X 250.

04-00 Muscular tissue••

The cells， whose protoplasmic property of contractility is highly developed， are called muscle cells， and the tissue consisting ofmuscle cells is the muscular tissue. As the muscle cells are elongated in the direction of contraction， they are usually calledmuscle fibers. Each muscle fiber is enclosed by reticular ( argylophilic ) fibers， connec- ted with these fibers and constitutes themuscular tissue.
Two categories of muscle are recognized according to the presence or absence of regular transverse bands along the length of
the fibers: striated and smooth. Striated muscle is subdivided into two distinct types， skeletal and cardiac. The fibers of skeletal
muscle are syncytial. The fibers of cardiac muscle are made up， on the contrary to the skeletal muscle， of separate cellularunits.

04-001 Skeletal muscle••

The skeletal muscle fiber is a long cylindrical multinucleate cell， visible with the light microscope. Large umber of parallel muscle
fibers are grouped into fascicles， visible to the naked eye. The muscle fibers， the fascicles， and the whole muscle are each
invested by connective tissue that forms a continuous stroma. The muscle as a whole is enclosed by a connective tissue layer
called epimysium. Thin collagenous septa that extend inward， surrounding all of the fascicles， collectively comprise theperimysium， and the exceedingly delicate reticulum that invests the individual muscle fibers constitutes the endomysium.
The blood vessels supplying skeletal muscle course in the connective tissue septa and ramify into a rich capillary bed around theindividual muscle fibers. The capil- laries are sufficiently tortuous to permit their accommodation to changes in length of thefibers， by straightening during elongation and contorting during contraction.

04-01 Skeletal muscles， longitudinal section 1. Human
tongue， H-E stain， x 160.
•

These are human tongue muscle fibers. Skeletal muscle fibers are long cylindrical multinucleated cells ranging from 10 to 30 cm inlength and from 100 to 500μｍ in diameter. They stain with acid dyes very deeply and show a closely spaced transverse striation.
A fine longitudinal striation is also detectable; this is due to fine contractile fibrils， myofibrils， of about 1μm in diameter. The
cross striation of the muscle fiber is due to the fact that corresponding segments of the closely packed myofibrils are in register
across the entire width of the fiber. The nuclei locate in the periphery of the cell， i.e.namely， directly beneath the cell
membrane， sarcolemma.

04-02 Skeletal muscles， longitudinal section 2. Monkey，
H-E stain， x 250.
•

In this figure the cross striation is distinct; a dark stained band alters with pale stained band regularly.

04-03 Skeletal muscles， longitudinal section 3. Human
tongue， H-E stain， x 400.
••

The cross striation consisting of the dark stained band and the pale stained bands is very distinct. The dark bands are anisotropic( birefringent ) and called A-bands and the pale bands are isotropic and called I-bands. The relative length of the bands depends
on the state of contraction: The length of the I-bands becomes very short during contraction， longer during relaxation， and thatof the A-bands remains constant in all phases. In the middle of the I-bands a thin transverse line crosses across the whole widthof the muscle fiber， that is the Z-line or Z-disc. The segments of myofibrils between successive Z-lines are called sarcomeres
and all of the morphological changes during the contractile cycle are described with reference to this structural unit.
The peripheral location of the nuclei， just beneath cell surface is very distinct.

04-04 Skeletal muscles， longitudinal section 4. Rat，
Heidenhain’s iron-hematoxylin stain， x 500.
•

This is the rat soleus muscle， stretched out and fixed. Heidenhain's iron-hematoxylin stains A-band especially deep. The I-bands
are longer than usual and the Z-lines are conspicuously noted. In the middle of the deeply stained A-bands， a thin pale band，
crossing the whole muscle fiber， is perceived， that is named H-band..

04-05 Scheme showing ultrastructure of a myofilament.

•

•

•
•

The myofibrils are the smallest units of the contractile material of muscle， that are visible with the light microscope， but inelectron micrographs， these are found to be composed of even smaller units， the myofilaments. These are of two kinds， thin
actin filaments and thicker myosin filaments. The cross-banded pattern of striated muscle is due to a highly ordered arrangementof interdigitating sets of these filaments.
Myosin filaments， 1.5μm in length and 15 nm in diameter， are oriented longitudin- ally in parallel array and spaced about 45 nm
apart. They are the principal constituent of the A-bands of the sarcomeres. Each is slightly thicker in the middle and tapers
toward its end. This thicker central portions cause a thin linear density called M-line that bisects paler H-band at the middle ofeach A-band.
Actin filaments， 1.0μm in length and 5 to 7 nm in diameter， are the dominant component of the I-bands， but at their ends，
they interdigitate with myosin filaments in the neighboring A-bands to varying degrees depending on the state of muscle
contraction. At their another ends the actin filaments attach to the Z-band.
This figure shows the relaxed state of the myofilament; the I-band is composed of actin filaments alone， the A-band， of bothinterdigitating actin and myosin filaments， causing the birefringency， and the H-bad consists of myosin alone. At contraction，interdigitating actin filaments slide into the myosin area deeply from both sides， causing the shortening of the entire length ofthe muscle fiber. In this state the I-band becomes very short and H-band disappears.

04-06 Skeletal muscle fibers， transverse section 1.
Human， H-E stain， x 500.
•

This is a skeletal muscle fiber bundle， fascicle， consisting of several muscle fibers.. The individual fibers are enclosed by
endomysium. In transverse sections， most of the interior of the individual fiber is occupied by myofibrils， 1 to 2μｍ in diameter.
They are resolved as fine dots either uniformly distributed or grouped in polygonal areas called the fields of Cohnheim. The
peripheral location of nuclei is clear.

04-07 Skeletal muscle fibers， longitudinal section. Endomysium 1.
Human， Silver impregnation and Kernechtrot stain， x 250.
•

Each skeletal muscle fiber is directly surrounded by reticular fibers; this coat is called endomysium. In this figure twolongitudinally sectioned skeletal muscle fibers are shown， whose surface is wrapped by the argylophilic fibers， that’s
endomysium.

04-08 Skeletal muscle fibers， longitudinal section. Endomysium 2.
Human， Silver impregnation and Kernechtrot stain， x 250.
•

This is a surface view of a skeletal muscle fiber. The endomysium wrapping the muscle fiber appears as relatively dense networkon the surface of the muscle fiber.

04-09 Skeletal muscle fibers， transverse section 2.
Human， Silver impregnation and Kernechtrot stain， x 400.
•

This is to show the endomysium consisting of reticular fibers， directly wraps the individual fiber. Arrows indicate blood vessels
containing erythrocytes.

04-10 Muscle spindle 1. Human， H-E stain， x 64.

•
•

•
•

This is a muscle spindle ( arrow ) found in the human thyreohyoideus muscle.
For muscles to be used in a coordinated manner for locomotion and other voluntary movement， the central nervous system
continuously needs information about the position of the limbs and the state of contraction of the various muscles. Such sensory
inputs are collectively called proprioception. To meet this need muscles contain complex sensors called neuromuscular spindles (muscle spindles ).
The muscle spindle consists of several modified thin striated muscle fibers enclosed in a fusiform capsule. They are 5 to 10 mmlong and therefore much shorter than the surrounding muscle fibers.
The specialized muscle fibers in the interior of the spindle are referred to as intra- fusal fibers to distinguish them from theunspecialized extrafusal fibers. The intrafusal fibers， from 6 to 12. in number， are kept in the central portion of the fusiform
cavity filled with a gelatinous substance.

04-11 Muscle spindle 2. Human， H-E stain， x 160.

•

Higher magnification of 04-10. The morphological differences between the intrafusal and extrafusal muscle fibers are conspicuous.
The capsule of the muscle spindle is incorporated in the perimysium enclosing the exstrafusal muscle fibers.

04-12 Muscle spindle 3. Rat， monoclonal antibody
reaction using synaptophisin， x 130.
••

The nerve endings on the intrafusal muscle fibers are visualized by a monoclonal antibody reaction using synaptophisin. The
afferent nerve fibers end on the intrafusal muscle fibers making spirals around them.
This preparation was made by Prof. Dr. A. Mizoguchi.

04-13 Motor nerve endings 1. Monkey tongue， silver
impregnation， x 64.
••

The skeletal muscle is innervated by craniospinal motor nerves. Nerve fibers， coming into the muscle fiber bundles， ramify andlose the myelin sheath， then attach to the muscle fibers， forming the motor nerve endings.
This figure shows a part of tongue muscle of monkey， silver impregnated. One nerve fiber bundle runs from bottom left to top
right. In the center this sends 3 branches to the muscle fiber bundles.

04-14 Motor nerve endings 2. Monkey tongue， silver
impregnation， x160.
•

This is a surface view of 4 nerve fibers， attaching to one muscle fiber forming the terminal branches， axon endings. Groups ofround or oval nuclei around the terminal branches are of Schwann cells which constitute the covering， hill of Doyere.

04-15 Motor nerve endings 3. Monkey tongue， silver
impregnation， x400.
•

This is also a surface view of one nerve fiber， terminating on one muscle fiber. One myelinated nerve fiber comes form bottom
right upwards， turns to left and ramifies to form the end plates on the surface of a muscle fiber. In the center， the terminal
branch- ings and their covering are conspicuous. The long arrow indicates myelin sheath and Schwann cell nucleus and the shortones capillaries.

04-16 Capillaries in the skeletal muscle fibers. Cat，
infusion of India ink， x 100.
•

The skeletal muscle is very rich in the blood supply. This is a part of the skeletal muscle fibers infused with India ink to visualize
the capillaries. The specimen is counter stained with carmine. Most of capillaries run longitudinally between the muscle fibers.

04-17 Muscle-tendon junction 1. Monkey， H-E stain，
x 160.
••

The force generated by contraction of a muscle is transmitted to its insertion through a tendon. The specialized region of
attachment at the interface between muscle cells and the bundles of collagen fibrils comprising the tendon is called themyotendinous junction. At the end of muscle fibers there are very large number of anastomising folds and cylindrical processes
that interdigitate with the collagen fiber bundles of tendon. These folds and processes are enclosed by the reticular fiber
network very tightly and they interdigitate with collagen fibrils of tendon， also tightly enveloped by the reticular fiber network.
The reticular fibers of both sides connect with each other so tightly that the myotendinous junction is very firm.
This figure shows the part where 4 skeletal muscle fibers pass into the tendon fibers. The end of the skeletal muscle fibers withcross striation gradually loses the striation and passes into the tendon fibrils.

04-18 Muscle-tendon junction 2. Monkey， H-E stain，
x 160.
•In this figure 3 skeletal muscle fibers attach obliquely to the periosteum， occupying bottom right one third of this field. The lower
end of the skeletal muscle fibers spread out， pass into collagen fibrils and attach to the periosteum.

04-002 Cardiac muscle•

The heart consists exclusively of specialized striated muscle， the cardiac muscle. The cardiac muscles exist only in the heart，and differ in several aspects from skeletal muscle fibers:①. Cardiac muscle consists of separate cellular units 10 to 20μｍ in diameter and 50 to 150μｍ in length. They are joined end
to end by special surface specializations， intercalated discs， that run transversely across the muscle cells.
②. The cardiac muscle cells form strands so predominantly parallel， but the indivi- dual cells branch and form obliqueinterconnections with neighboring strands resul- ting in a complex three dimensional organization ( network ).
③. The elongated nuclei of the cellular units are usually situated deep in the axial portion of the cells， instead of immediately
beneath the sarcolemma.
④. The cardiac muscle beats spontaneously and its rhythmical contraction is not subject to voluntary control.

04-19 Cardiac muscles， longitudinal section 1. Human，
H-E stain， x 250.
•

This is a longitudinal section of cardiac muscles. The cardiac muscle cells are cylindrical in shape， and have an elongate nucleus
in the middle of each cell. The myofibrils with cross striations are less numerous than in the skeletal muscle fibers and the
granular cytoplasm， sarcoplasm， is distinctly recognized juxtanuclear region. The cells connect end to end with special surface
specialization， the intercalated discs ( long arrows ) and form long parallel strands. At the center of this figure an obliqueinterconnection between the neighboring cells ( short arrow ) is seen. The meshes of the network of the cardiac muscle cells arefilled by very loose connective tissue containing numerous capillaries.

04-20 Cardiac muscles， longitudinal section 2. Human，
H-E stain， x 250.
•

In this figure a collateral branch of cardiac muscle cell and its connection with the neighboring cell are conspicuous. Arrow
indicates the intercalated disc on this connection.

04-21 Cardiac muscles， longitudinal section 3. Human，
M-G stain， x 250.
•

In this specimen reticular fibers wrapping the individual muscle cell are stained blue and intercalated discs dark blue distinctly. In
the loose meshes made by the cardiac muscle cells capillaries containing erythrocytes are conspicuous.

04-22 Cardiac muscles， transverse section 1. Human，
H-E stain， x 160.
•

This is a transverse section of cardiac muscle cells. The contour of the individual cells is round or polygonal and the central
position of their nuclei is evident.

04-23 Cardiac muscles， transverse section 2. Human，
M-G stain， x 250.
•

The interior of cardiac muscle cell is filled with myofibrils and in the middle of it locates a nucleus. The surface of the individual
cells is enveloped by reticular fibers stained green. Among the muscle cells there are numerous capillaries.

04-24 Cardiac muscles， specialized conducting fibers 1.
Human， M-G stain， x 64.
•••

The beats of heart start from the specialized region， sinoatrial node. To function effectively as a pump， the contraction of theatria must be completed slightly before the onset of ventricular contraction. The precise timing and coordination of events in the
cardiac cycle depends on myocytes that are specialized for initiation of excitation and its conduction to different regions of the
myocardium at a rate that will ensure their activation in the correct sequence.
These specialized cardiac muscle cells establish a special conducting system consis- ting of sinoatrial node， atrioventricularnode， internodular tracts， and atrioventricular bundle， dividing into right and left bundle branches that ramify beneath theendocardium of the right and left ventricles， establishing communicating junctions with the unspecialized working cardiac
muscles.
This figure shows a part of the conducting system beneath the endocardium of the atrium. The connective tissue underlying theendocardium stains green; directly beneath it， there are two kinds of cardiac muscle bundles， the upper consisting thick muscle
cells are the conducting system and the lower the working cardiac cells. As the cardiac cells of the conducting system containless numerous myofibrils they stain lightly red whereas the unspecialized working ones contains much myofibrils and stain dark
red. At lower surface of the conductive system the communicating junctions are recognized.

04-25 Purkinje fibers. Bovine， H-E stain， x 64.

•

In the bovine heart the conducting system consists of thick fibers， called Purkinje fibers. The lower half of this figure is occupiedby the Purkinje fibers; they are very thick containing small nuclei. The muscle cells of the upper half of this figure areunspecialized working cardiac muscle cells.

04-26 Cardiac muscle fibers，specialized conducting
fibers. Human， M-G stain， x 160.
•

The muscle cells of the conducting system contain less numerous myofibrils， as are seen here. The surface of the cells is
enveloped by the reticular fibers. In this figure the intercalated discs are conspicuous.

04-27 Cardiac muscle fibers， specialized conducting
fibers. Human， H-E stain， x 250.
•

The longitudinal sections ( top ) and transverse sections ( bottom ) of the specialized conducting cardiac muscle cells are shown.

04-28 Junction between specialized conducting fibers
and normal cardiac fibers. Human， H-E stain. X 160.
•

The specialized conducting cells ( left half ) are making the communicating junctions with the unspecialized working cardiac
muscle fibers ( right half ).

04-003 Smooth Muscles

•

•

•

The smooth muscle fibers are long fusiform or spindle-shaped with their elongated nucleus situated in their wider central
position. They vary greatly in their length in different organs. In gravid human uterus smooth muscle fibers may reach a length of
0.5 mm， in the wall of the intestine their average length is about 0.2 mm， and in the wall of blood vessels， the smallest smoothmuscle fibers may be only 20μｍ long.
Where smooth muscle fibers is organized in bundles or extensive layers， the individual fibers offset such the wide portion of thecells are adjacent the thin tapering ends of neighboring cells. So， in the transverse sections， smooth muscle appears as amosaic of rounded or polygonal profiles varying from one to several microns in diameter， with nuclei found only in the larger
profiles.
The cytoplasm stains with acid dyes deep homogeneously and no cell organells nor fibrils with cross striation are perceived. The
individual smooth muscle fibers are wrapped densely by reticular fibers and connected together with neighboring fibers.

04-29 Smooth muscle fibers， longitudinal section.
Human， H-E stain. X 160.
•

These are smooth muscle fibers of the human duodenum. Individual fibers are long spindle-shaped and stain homogeneously deep
red with eosin. Nuclei locate in their wide portion. Nappy fibers between the muscle fibers are reticular fibers.

04-30 Smooth muscle fibers， longitudinal section.
Monkey， H-E stain. X 250.
•

These are also smooth muscle fibers of the intestine. They are somewhat contracted， so the nuclei shows uneven contour. The
reticular fibers connecting the muscle fibers are very conspicuous as nappy fibers.

04-31 Smooth muscle fibers， longitudinal section.
Human， silver impregnation and Kernechtrot stain. X 250.
•

These are smooth muscle fibers of human esophagus， silver impregnated. The reticular fibers wrapping the individual muscle
fibers are blackened. The muscle fibers are connected with neighboring fibers by the blackened fibers. The specimen was counterstained with Kernechtrot.

04-32 Smooth muscle fibers， transverse section. Human，
H-E stain. X 160.
•

This is transverse section of a smooth muscle bundle of the human stomach. It shows a mosaic pattern of polygonal profiles ofthinner and thicker sections of muscle fibers. Only a few large profiles contain nuclei.

04-33 Smooth muscle fibers， transverse section. Human，
H-E stain. X 400.
•

Higher magnification of 04-32. The nappy fibers connecting the individual muscle fibers are conspicuous.

04-34 Smooth muscle fibers， transverse section. Human，silver impregnation and Kernechtrot stain. X 250.
•

The individual muscle fibers are enclosed by reticular fiber， black line， so the mosaic pattern of polygonal profiles of thinner andthicker sections of muscle fibers is distinct. The arrows indicate the perimysium， consisting of collagen fibers， not blackened
but colored deep brown.