Skeletal Muscles Dissection

8/13/2019 Skeletal Muscles Dissection

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Musculature

Guide


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ats! MusculatureTHROUGHOUT THE FOLLOWING DISSECTION OF THE MUSCLES, EXCEPT WHERE

SPECIFIED, DISSECTION IS TO BE CONFINED STRICTLY TO THE CATS RIGHT SIDE. LEAVETHE LEFT SIDE INTACT FOR THE LATER DISSECTION OF OTHER SYSTEMS.

From here o ! "he #!$$e%"!o, &$e ' $m'(( )o""(e o* +'"er '# ' ee#ro--er "o-er!o#!%'(( mo!$"e "he -'r"$ o* o&r $-e%!me "h'" h'e )ee %&".

Muscles of the abdominal wall

The abdominal wall is composed of three layers of muscles, with their associated and quite extensiveaponeuroses.

[Aponeurosis = loos lie! " nerve! = a whitish, fibrous membrane actin# as a tendon sheet$ it may attach themar#in of a muscle sheet to its ori#in or insertion%which may be a bone or another aponeurosis$ or it may &ointwo muscles alon# their shared len#th, thus stabili'in# their relationship in a combined action.(

The three layers of the abdominal wall are)*an outermost layer, the external oblique$

*a middle layer, the internal oblique$*and an innermost layer, in two parts)

+ medially, the rectus abdominis (runnin# from sternum to pubic bone, underneath thetwo layers of aponeuroses by which the obliques insert

on the linea alba$ + laterally, the transversus abdominis-extendin# laterally from the ed#es of the rectus.

External oblique. This is the lar#e muscle sheet constitutin# the superficial layer of the abdominalwall. Be sure to clean away any remaining superficial fascia or fat from its surface.* ts anterior dorsalportion is partially concealed under the lar#e, flat latissimus dorsi. [The latissimusori#inates from the spinous processes of the vertebrae and their associated fascia in the middorsal line, passesanteriorly and ventrally, coverin# much of the upper bac, and inserts on the proximal humerus .( /ompletelyloosen the latissimus by #ently thrustin# fin#ers between the two muscles, worin# bac and forth,pushin# dorsally until the fin#er shows throu#h its sheet tendon -the most superficial layer of thelumbodorsal fascia. 0ow locate the posterior boundary of the latissimus dorsi$ carefully slit alon#the dorsal mar#in of its muscle tissue, leavin# its sheet tendon in place. -ts sheet tendon is the mostsuperficial layer of the lumbodorsal fascia. 1ift the latissimus away from the surface of the externaloblique. Any fat present between the two muscles should be cleaned away. ith its total exposure,now it can be seen that the external oblique 3450AT67 from the lumbodorsal fascia and posteriorribs$ its fibers pass obliquely ventral and posteriorly$ and it 0764T7 by an extensive band ofaponeurosis on the linea alba.

Internal oblique. 8sin# the scalpel, very carefully -very thin slice transect only the external

oblique for a distance of 9:;< cm in the abdominal area. [Transect means: cut across the fibers at aright angle, through the belly, or middle, of the muscle. ] f there is a sur#ical cut on one side of theabdomen, that would be a #ood place to start from. 8se the blunt metal probe to separate ;cephaladand 0764Tby an extensive band of aponeurosis on the linea alba. A/T30) compression of theabdomen.


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Transversus abdominis. @ery carefully transect 2:? cm of the internal oblique and separate theed#es of the cut. A third, fairly thin muscle layer will be found, the transversus abdominis, the fibersof which run ventrally and slightlyposteriorly. 3450) the lumbodorsal fascia. 0764T30) by anarrow aponeurosis on lateral mar#in of the rectus abdominis. A/T30) compression of theabdomen.

Show your teacher the three different layers of the abdominal wall.

Rectus abdominis. This is a pair of lon# slender muscle #roups on either side of the ventralmidline, extendin# from the pubic symphysis all the way to the sternum. t is found &ust under theinsertion aponeuroses of the obliques, and between the medial mar#ins of the transversus. /arefully-very thin slice slit the aponeuroses alon# the ed#e of the linea alba, and fold them laterally to exposethe rectus. ts fibers run lon#itudinally, and in the cat are crossed at re#ular intervals by white lines,the myosepta -muscle partitions!. [In humans, the rectus is much broader, and the myosepta are moreprominent; a well developed rectus in a human is known as a six-pack.] 3450) sternum and costalcartila#es. 0764T30) anterior mar#in of the pubic symphysis. A/T30) constriction of the abdomen-adduction of the pelvis, and some compression of the abdomen.

Superficial muscles of the chest

6xpose the chest by spreadin# the forelimbs and fastenin#>wei#hin# them down if necessary. The

#reat muscles coverin# the ventral side of the thorax are the pectoral roup. A/T30 of the #roup)adduction of the forearm toward the chest. The #roup is divisible into four portions which are notalways easily separable from each other. o your best to reco#ni'e their mar#ins, and separate themfrom each other for several centimeters alon# their respective mar#insusin# your blunt probe. -7howteacher when finished. Brom front to bac they are)

!ectoantebrachialis. -from chest to front side of arm! The most anterior and superficial of thepectoral #roup. 3450) manubrium. 0764T30) by flat tendon, on the deep fascia of the upperarm.


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!ectoralis ma"or. The next posterior muscle$ but its anterior mar#in underlies thepectoantebrachialis. 3450) sternum and median ventral raphe -which are the lateral mar#ins of thelinea alba in the thoracic re#ion. [ raphe !ray" #ee$ is a very narrow aponeurosis, so it appears as a thinwhite line between muscles; the cat%s myosepta mentioned above are raphes.] 0764T30) on thehumerus. To see this insertion, transect the pectoantebrachialis and fold the cut distal portion aside.

!ectoralis minor. 0ext posterior$ but a#ain, its anterior portion is lar#ely covered by the pectoralisma&or. 3450) sternum. 0764T30) on the humerus -but this insertion cannot be fully traced atthis sta#e of the dissection.

#iphihumeralis. A lon#, thin, flat muscle 3450AT05from the xiphoid process of the sternum,with its anterior part passin# dorsal -interior to the posterior portion of the pectoralis minor.4emainin# strands of the cutaneous maximus may be present on its surface. 0764T30) on thehumerus$ the insertion is probably covered by fatty tissue in the axilla.

Muscles of the ventral nec$ and throatIf not done during skinning: Slit the skin at the midline of the throat, all the way to the midpoint of the mandible.

Loosen this skin by separating it from the deep fascia with firm strokes of the back of the scalpel tip

and/or the blunt probe. Then remove the two halves of it completely so as to expose fully the ventral surface of the jaw

all the way out to the left and right margins of the mandible, over the angles and rami of the mandible, and close around

the posterior base of each pinna. !"n doing so, note parts of the platysma on the underside of the skin and superficial

fascia. #hen intact, the platysma swept from the median dorsal line of the neck around the sides of the head to the face$

also, portions of it may have originated from the pectoral group near the anterior end of the sternum.%

CAUTION! In dissectin& the throat muscles, continue to work on the ri&ht side only, except where speci#icallydirected di##erently, leavin& the le#t side intact #or the study o# other systems later. 'specially avoid cuttin& anylar&e blood vessels unless instructed to. (e sure the skin is completelyremoved #rom under the )aw; all the

way out to the lateral sur#ace o# the mandible, and thoroughlyclean away any remainin& bits o# hypodermisand #at.

De#in by inspectin# the ventral nec and throat area. At the an#le of the &aw is a rounded, #ranular,pinish body, the submaxillary salivary land, crossed by the posterior facial vein. Detweenthis #land and the ear is a lar#er, similar looin# mass, theparotid salivary land. The posteriorfacial vein &oins a lar#er vein, the external "uular vein, which runs posteriorly in the superficialmuscles of the throat, crossin# the ventral face of the sternomastoid muscle. The transverse

"uular veincrosses the throat, connectin# the heads of the two external &u#ulars near the ends ofthe posterior facials. 3ther smaller, paler, smoother bodies are liely to belymph lands. 0ow findthe followin# muscles)


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%iastric. The thic dia#onal muscle attached to the medial surface of the mandible is the di#astricFosteriorly, it passes under the submaxillary salivary #land. 3450) &u#ular and mastoid processesof the sull. 0764T30) on the mandible. A/T30) prime mover for depressin# the mandible-antagonist of the massetersee next.

&'TE ) of the next * muscles (exceptin the sternomastoid+ are responsible for the swallowin

mechanism in advanced mammals.

Masseter. This is the #reat thic muscle coverin# the an#le of the &aw, situated &ust anterior to thesubmaxillary and parotid #lands. The parotid #land duct should be seen passin# over the surface ofthe masseter$ branches of facial nerves may be seen at the superior and inferior mar#ins of themasseter. 3450) 'y#omatic arch. 0764T30) on the posterior portion of the lateral surface of themandible. A/T30) prime mover for elevation of the mandible -antagonist of the digastric, justdescribed.

Mylohyoid. This is the thin transverse sheet passin# across from one mandible half to the other,between and internal to the two di#astrics. 3450) medial surface of the mandible -concealed by thedi#astrics. 0764T30) on their own median raphe. A/T30) raises and stiffens the floor of themouth -forcin# the advancin# ton#ue a#ainst the palate, enablin# the ton#ue to exert upward andbacward pressure that forces the food bolus into the pharynx$ also, indirectly helps pull the hyoidbone forward, by pressin# upward on the #eniohyoids -see next. [This is the secondary componentof thestae , of the swallowin action.(

Sternomastoid. This is the prominent superficial muscle of the ventrolateral nec. The external&u#ular vein crosses its surface at an an#le to the direction of its fibers. 3450) by two parts%superficially, from the median raphe$ and &ust deeper, from the manubrium. t then passes forward,diver#in# from the midventral line, passin# around the side of the nec and beneath the submaxillaryand parotid #lands, to where it0764T7on the sull, both on the superior nuchal line and by thictendon onto the mastoid process. A/T30) acting singly, turn the head$ acting together, flex the

head toward the chest. [In humans, this is a compound muscle with the cleidomastoid*see below*so inhumans it is called the sternocleidomastoid.]

+' he next two muscles are listed in the order they may be most easily dissected and observed, #romsuper#icial to deep. (ut in the swallowin& action se/uence, the thyrohyoids act #irst !sta&e 0$ and thesternohyoids and sternothyroids act last !sta&e 1$.

Sternohyoid. The posterior portions of this muscle pair are visible between the two sternomastoidsas the latter diver#e from the median raphe at the manubrium. Carefully slit the extreme ori#ins-medial of the ri#ht pectoantebrachialis, pectoralis ma&or, and sternomastoid. Bold thesternomastoid up and to the side, thus exposin# the full len#th of the ri#ht sternohyoid. /losely

united to each other alon# the midventral line, the sternohyoids extend from their 3450on the firstcostal cartila#e to their 0764T30on the body of the hyoid bone. A/T30) draw the hyoid boneposteriorly, restorin# it to its rest position after swallowin#. [This is one component ofstae ) ofthe swallowin action, complementin# the action of the sternothyroids%see next.(

Sternothyroid. Carefully dissect and reflect the mylohyoid and sternomastoid, and reflect bothhalves away to the side. 0ow it can be seen that the sternothyroid muscles are located, one on eachside of the trachea, &ust deep to the sternohyoids. Gently use your fin#er to push the belly of theri#ht sternothyroid sli#htly laterally. This exposes the trachea -windpipe!, a tube stiffened by rin#s


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of cartila#e. At the anterior end of the trachea is a chamber with cartila#inous walls, thelarynx-voice box!. The chief cartila#e of the larynx is the lar#e, shield:shaped thyroid cartilae, formin#the larynxG ventral wall. Hust anterior to the thyroid cartila#e, the body of the hyoid bone can be felt a

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a bony bar on which the sternohyoids insert. 7ternothyroid 3450) first costal cartila#e, in commonwith the sternohyoids. 0764T30) thyroid cartila#e of the larynx. A/T30) draw the larynxposteriorly, restorin# it to its rest position after swallowin#. [This is the other component ofstae )

of the swallowin action, complementin# the action of the sternohyoids -see above$ and by reflexarc, initiatin# esopha#eal peristalsis.(

-leidomastoid. solate the ri#ht sternomastoid$ if you did not completely separate it from itsori#ins at the manubrium and median raphe, then transect it at this time, and fold the two ends away.8sin# the blunt probe, separate and loosen the clavotrape'ius$ internal to it, &ust deep and dorsal tothe sternomastoid, find a narrow flat muscle, the cleidomastoid. This muscle attaches to the medialhalf of the clavicle, and to the mastoid process, &ust dorsal to the insertion of the sternomastoid.

A/T307) actin# with the clavotrape'ius, it pulls the clavicle craniad$ actin# with the sternomastoid,turns head and>or lowers face toward nec. Thus, 3450and 0764T30are functionally chan#eable.[In humans, this muscle is #used with the sternomastoid, and is called the sternocleidomastoid.]

Muscles of the medial thih

The medial surface of the thi#h is covered by two lar#e, flat, superficial muscles. Doth muscles inserton the proximal end of the tibia. TheSartorius, which occupies the anterior half, ori#inates at theilium and is responsible for adductin# and rotatin# the thi#h. The racilis, which covers most of the

posterior surface, ori#inates at the ischium and pubic symphysis and also adducts the thi#h. /arefullytransect both muscles across the middle and reflect their cut ed#es to expose the underlyin# muscles.

Semimembranosus.A very thic muscle lyin# deep to the #racilis. t is divided throu#hout most ofits len#ths into two portions. 3450) schium. 0764T30) distal end of the femur. A/T307)extendin# thi#h.

/dductor femoris. This lar#e trian#ular muscle lies deep to the #racilis and proximal to thesemimembranosus. 3450) schium and Fubis. 0764T30) shaft of the femur. A/T307)extendin# thi#h.


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Rectus femoris.1ar#ely covered by the sartorius, this muscle is lon# and round. To#ether, with thevastus medialis, lateralis, and intermedius, it maes up the quadriceps femoris muscle. 3450)Bemur. 0764T30) Fatella. A/T307) Adducts thi#h

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0astus lateralis.1ies beneath the fascia lata alon# the anterior ed#e of the thi#h. 3450) Froximapart of the femur. 0764T30) Fatella. A/T307) 6xtends le#

With the cat on its back, complete a sketch of the following ventral muscles and structures:!Be sure to illustrate the directions of each muscle fiber)

'xternal obli/ue Internal obli/ue ransversus abdominis 2ectus abdominis3ectoantebrachialis 3ectoralis ma)or 3ectoralis minor 4iphihumeralis

5i&astric 6asseter 6ylohyoid 7ternomastoid7ternohyoid 7ternothyroid 8racilis 7artorius2ectus #emoris 7emimembranosus

Before studying the dorsal muscles, familiarize yourself with the appearance and orientationof the cats vertebrae, scapula, and dorsal skull! and re"familiarize yourself with the specificnames of the following skeletal features :

# principle vertebral processes# all parts of the scapula# dorsal$posterior skull features.

%ow, turn the cat to place it belly down on the table, with its tail to your left and its head toyour right.

Superficial muscles of the dorsal nec$1 shoulder1 and upper bac$

Trape2ius muscle roup. These are the shallow -flat muscles coverin# the anterior bac and thebac of the nec. n humans these are a sin#le lar#e muscle, but in the cat they are divided into three.Brom front to bac...

* -lavotrape2ius. Hust lateral and dorsal to the sternomastoid is a lon#, flat muscle on the side ofthe nec which appears to pass over the ventral surface of the shoulder to the forearm. This is


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sometimes considered as one lon# continuous muscle -called the cephalobrachialis. Dut since ithas insertions on the lateral end of the clavicle, it is more usually treated as two muscles, and we willtreat it that way here. The broad, trian#ular, superior part which passes from the dorsal nec to thetip of the shoulder is called the clavotrape2ius. t 3450AT67from the superior nuchal line of the

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occipital bone and from the dorsal midline nec -where the left and ri#ht clavotrape'ius are &oined bya thin raphe, passes obliquely ventrally and posteriorly, and 0764T7on the lateral portion of the

clavicle, which is embedded on its inside surface. A/T30of the clavotrape'ius) draws the clavicledorsad and craniad. [The inferior part of the cephalobrachialis is called the clavobrachialis, which3450AT67 from the lateral portion of the clavicle and passes all the way down to 0764T30on the ulna.

A/T30of the clavobrachialis) flexion of the arm. See forelimb discussion below.(

*/cromiotrape2ius. These are the lar#e but thin, trape'oid:shaped, central muscles of thetrape'ius #roup. They are attached to each other by a thin aponeurosispass directly between thescapulae, stabili'in# the relationship and limitin# the lateral travel of those bones in the upri#ht cat.They have sheet tendons on their mar#ins as follows) anteriorly, attachin# them to the posteriorborder of the clavotrape'ius$ medially, attachin# them to each other, and to their 3450 on thespinous processes of the last cervical and first thoracic vertebrae$ andposteriorly-&oinin# them tothe spinotrape'ius%next muscle described. 1aterally they appear simply to stop at the spine of the

scapula. 0764T30) on the spine of the scapula, especially near the acromion process. A/T30) drawscapula dorsad and hold the two scapulae to#ether.

*Spinotrape2ius. This is the trian#ular, most posterior trape2ius muscle. 3450) on thespinous processes of the thoracic vertebrae$ passin# obliquely forward and coverin# part of thelatissimus$ 0764T30on the spine of the scapula and surroundin# fascia. A/T30) draws thescapula dorsad and caudad.

3atissimus dorsi. The lar#e #enerally flat muscle extendin# obliquely forward from the middle ofthe bac to the upper arm. -Kou may have already slit this muscle at its ori#in when you studied theexternal oblique. 3450) mainly from the lumbodorsal fascia, but also from the dorsal processes ofthe last thoracic and first lumbar vertebrae. 0764T30) by tendon, on the medial surface of the

humerus. A/T30) pulls the upper arm dorsad and caudad.

%eltoid muscle roup. A/T30) deltoid muscles raise and rotate the humerus. [9e will say there aretwo deltoids in the cat. 7ome authorities say there are three they also consider the clavobrachialis!described above in the clavotrapezius discussion$ to be a deltoid, since it contributes to elevation o# the arm;and so they call it the clavodeltoid. thers, includin& mysel#, believe that the clavodeltoidians are allowin&human anatomy to in#luence their interpretation o# the cat*since, as both camps a&ree, the clavobrachialis,acromiodeltoid, and spinodeltoid muscles may be considered homolo&ous with the sin&le deltoid muscle o#humans.]

* The acromiodeltoidis a short, thic muscle havin# its 3450on the acromion of the scapula$ itpasses ventrally under the levator scapula, and out to its 0764T30on surfaces of other muscles ofthe shoulder. t lies lateral and posterior to the clavobrachialis [or clavodeltoid(.

* The spinodeltoidis tricier) The spinodeltoid 3450AT67on the spine of the scapula, underliesthe levator, passes to the upper arm, and0764T7on the deltoid rid#e of the humerus -insertionconcealed by the acromiodeltoid.


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&ow1 "ust as you did for the latissimus dorsi1 carefully and completely slit all threeriht4side trape2ius muscles/&$" "o "he r!0h" o* their oriins alon the dorsal midline.5old them down laterally6ventrally to expose the deep muscles of the dorsal thorax.

%eep muscles of the dorsal thorax

3evator scapulae ventralis. Alon# the anterior border of the acromiotrape'ius, and apparentlycontinuous with it near its insertion, is seen a flat, band:lie muscle which passes anteriorly, diver#in#from the acromiotrape'ius and passin# internal to the clavotrape'ius -now cut. This is the levatorscapulae ventralis -ventral lifter of the scapula!. -f it seems odd that this muscle is called ventral,consider that the other muscles which can elevate the scapula, namely the trape'ius #roup, are allmore dorsal than it is. 3450) occipital bone and transverse process of the atlas. 0764T30)metacromion process of the scapula and nei#hborin# fascia.A/T30) draws the scapula craniad.[+ote this muscle has no homolo&ue in humans.]

Rhomboideus. Bold down the spino: and acromiotrape'ius muscles. A set of thic muscle strandswill be seen beneath them, extendin# from the middorsal line to the vertebral border of the scapula.This is the rhomboideus. 3450) transverse processes of the thoracic vertebrae and ad&acent

li#aments. 0764T30) vertebral border of the scapula. A/T30) draw the scapula dorsad. The mostanterior portion of this muscle is practically a separate muscle, therhomboideus capitis[nohomolo#ue in humans(, which extends as a slender band forward to its 3450 on the superior nuchalline. 0764T30) scapula. A/T30) draw the scapula craniad and rotate it.

The next ) muscles oriinate on the scapula and act on the humerus

Supraspinatus. Bold down the acromiotrape'ius to see a stout muscle occupyin# the supraspinousfossa of the scapula, from whose surface it taes its 3450. This is the supraspinatus. 0764T30)#reater tuberosity of the humerus, next to the insertion of the pectoralis minor. A/T30) extend thehumerus -draw it anteriorly.

Infraspinatus. f the latissimus dorsi is still attached posteriorly, separate it from its ori#in byloosenin# and slittin# its lumbodorsal sheet tendon. Drin# the latissimus and spinotrape'ius forwardso as to expose the posterior portion of the scapula. Two lar#e muscles are seen here. The anteriorone fills the infraspinous fossa of the scapula, from whose surface it taes its 3450, and is insertedon the #reater tuberosity of the humerus. This is theinfrapinatus. ts 0764T30is concealed bythe deltoids, which may be cut across to see it. A/T30) laterally rotate the humerus.

Teres ma"or the stout muscle immediately behind the infraspinatus, whose fibers run in the samedirection. 3450) posterioventral -axillary! border and medial surface of the scapula, and fascia ofnei#hborin# muscles. 0764T30) in common with the latissimus dorsi on the medial surface of thehumerus. A/T30) rotate the humerus and draw it posteriorly.


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Skeletal Muscles Dissection

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