=1. Muscles of the Back.=
A. MUSCLES OF THE SHOULDER (connecting the forelimb with the back) (Fig.
68).
=M. trapezius=.--The trapezius muscle is divided in the cat into three
portions, the spinotrapezius, the acromiotrapezius, and the
clavotrapezius.
=M. spinotrapezius=, or trapezius inferior (Fig. 68, _j_).--The
spinotrapezius (caudal part of the human trapezius) is a flat triangular
muscle.
_Origin_ from the tips of the spinous processes of all or nearly all the
thoracic vertebræ and from the intervening supraspinous ligament. The
origin may extend from a point anywhere between the first and fourth
spines to any point between the eleventh and thirteenth.
_Insertion_ along an S-shaped line (Fig. 76, _k_-_l_) which crosses the
tuberosity of the scapular spine and forms an angle with the spine of
about forty-five degrees. The line extends on one side onto the fascia
covering the supraspinatus muscle, and on the other side onto the fascia
covering the infraspinatus, but does not reach the borders of the
scapula. The cranial two-thirds of the insertion is by a flat tendon
which is broader craniad.
_Relations._--Outer surface with the cutaneus maximus, and craniad with
the acromiotrapezius (_h_). Inner surface with the latissimus dorsi
(_m_) caudad and with the rhomboideus, supraspinatus, and infraspinatus
craniad. Caudal border free; cranial border in contact with the
acromiotrapezius (_h_).
_Action._--Draws the scapula dorsocaudad.
=M. acromiotrapezius=, or trapezius superior (Fig. 68, _h_).--The
acromiotrapezius (middle part of the human trapezius) is a flat
four-sided muscle just craniad of the spinotrapezius, from the median
dorsal line to the scapular spine.
_Origin_ along the median dorsal line from the spinous process of the
axis to a point anywhere between the spinous processes of the first and
fourth thoracic vertebræ. Its caudal two-thirds is from a flat tendon
which is directly continuous with the muscle of the opposite side and
thus bridges the depression between the vertebral borders of the
scapulæ. This tendon narrows craniad, and its cranial fourth is attached
by a fascia to the spinous processes of the cervical vertebræ. At the
cranial border of the muscle the fibres sometimes reach the middle line.
The fibres of the muscle run nearly transversely.
_Insertion_ (Fig. 76, _h_).--Into the outer surface of the metacromion,
the glenoid border of the scapular spine from the metacromion to the
tuberosity, and along a line continued for about one centimeter from the
tuberosity onto the surface of the spinotrapezius (_j_) at the junction
of its muscular and tendinous portions.
[Illustration: FIG. 68.--FIRST LAYER OF BODY-MUSCLES, BENEATH THE SKIN
AND SKIN-MUSCLES.
_a_, M. frontoscutularis; _b_, M. masseter; _c_, M. sternomastoideus;
_d_, M. clavotrapezius; _e_, M. clavobrachialis; _f_, M. levator
scapulæ ventralis; _g_, M. acromiodeltoideus; _h_, M.
acromiotrapezius; _i_, M. spinodeltoideus; _j_, M. spinotrapezius;
_k_, caput longum of M. triceps brachii; _l_, caput laterale of M.
triceps brachii; _m_, M. latissimus dorsi; _n_, M. xiphihumeralis;
_o_, M. pectoralis minor; _p_, M. obliquus abdominis externus; _q_, M.
sartorius; _r_, M. tensor fasciæ latæ; _s_, M. caudofemoralis; _t_, M.
biceps femoris; _u_, M. semitendinosus; _v_, M. extensor caudæ
lateralis; _w_, M. abductor caudæ externus; _x_, M. flexor caudæ
longus; _y_, lumbodorsal fascia, superficial layer; _z_, fascia lata.
1, parotid gland; 2, submaxillary gland.]
_Relations._--Outer surface with the cutaneus maximus, the integument
and platysma. Inner surface with a mass of fat partially covering the
rhomboideus; with the occipitoscapularis, spinotrapezius, supraspinatus,
levator scapulæ, and splenius. Near its origin its caudal border touches
the outer surface of the spinotrapezius (_j_). Its cranial border is
overlaid near its insertion by the levator scapulæ ventralis (_f_) and
is closely related to the caudal border of the clavotrapezius (_d_)
near its origin.
_Action._--The two muscles hold the scapulæ together.
=M. clavotrapezius= (Fig. 68, _d_).--The clavotrapezius (cranial part of
the human trapezius) is a flat muscle passing from the lambdoidal crest
and middorsal line to the clavicle and covering the side of the neck.
_Origin._--The medial half of the lambdoidal crest and the middorsal
line between the crest and the caudal end of the spine of the axis. The
fibres are parallel and pass caudoventrad so that the muscle covers the
ventral surface of the neck caudally and fills the concavity at the
front of the shoulder.
_Insertion_ into the clavicle and into a raphe between the
clavotrapezius and the clavobrachial (_e_) muscles. This raphe extends
along the clavicle and for some distance laterad of it. The muscle is
partly continuous with the clavobrachial (_e_).
_Relations._--Outer surface with the platysma, and at its craniomedial
angle with the levator auris longus. Inner surface with the rhomboideus,
splenius, occipitoscapularis, levator scapulæ, cleidomastoid, and
supraspinatus. The cranial edge touches the sternomastoid. The caudal
border touches the acromiotrapezius near the origin.
_Action._--Draws the scapula craniodorsad.
This muscle and the clavobrachial (_e_) are sometimes considered as
forming a single muscle, the cephalohumeral, or cephalobrachial.
=M. occipitoscapularis= (or levator scapulæ dorsalis or rhomboideus
capitis) (Fig. 73, _a_).--The occipitoscapularis (equivalent to a part
of the human rhomboideus) is a slender flat muscle from the lambdoidal
ridge to the coracovertebral angle of the scapula.
_Origin_, the medial half of the lambdoidal ridge beneath the
clavotrapezius (Fig. 68, _d_). The origin does not extend quite to the
middle line. The muscle passes almost directly caudad. Its caudal end is
thicker and narrower than the cranial end and is wedged between the
rhomboideus dorsally and the levator scapulæ ventrally.
_Insertion_ either into the inner surface of the levator scapulæ near
its dorsocranial border at its insertion or into the scapula near the
coracovertebral angle (Fig. 78, _f_) or into both. Its fibres are very
closely related to those of the rhomboideus.
_Relations._--By its outer surface with the clavotrapezius (Fig. 68,
_d_) and acromiotrapezius (_h_). At its insertion it is often overlaid
by either the rhomboideus or the levator scapulæ or both. By its inner
surface with the splenius (Fig. 73, _b_). Its caudal third is wedged
between the rhomboideus and the levator scapulæ.
_Action._--Draws forward and rotates the scapula.
=M. rhomboideus= (probably equivalent to the human rhomboideus major and
rhomboideus minor).--A rather thick trapezoid muscle connecting the
vertebral border of the scapula with the spinous processes of the
adjacent vertebræ.
_Origin_ from the caudal two or three fifths of the cervical
supraspinous ligament and from the sides and tips of the first four
thoracic vertebral spines and the interspinous ligaments caudad of these
four spines. It passes lateroventrad, and the fibres converge somewhat
so that the line of insertion is shorter than the line of origin.
_Insertion_ by a short tendon (1 millimeter long) into the vertebral
border of the scapula, the line of insertion passing gradually from the
inner (Fig. 78, _e_) to the outer (Fig. 76, _i_) surface; and by fleshy
fibres into the outer surface of the glenovertebral angle of the scapula
(Fig. 76, _i_) in close connection with the origin of the teres major
(_j_). A bundle of fibres at the cranial border may be inserted into the
cranial border of the levator scapulæ at its insertion.
_Relations._--By its outer surface with the spinotrapezius (Fig. 68,
_j_), acromiotrapezius (_h_), latissimus dorsi (_m_), and clavotrapezius
(_d_); it is usually partially separated from these muscles by a mass of
fat. By its inner surface near its insertion with the serratus anterior
(Fig. 73, _i_) and levator scapulæ (Fig. 73, _h_), and craniad with the
splenius (Fig. 73, _b_), and the tendon of the serratus posterior
superior (Fig. 73, _l_). At its lateral end it touches the
occipitoscapularis (Fig. 73, _a_), serratus anterior (_i_), levator
scapulæ (_h_), supraspinatus (Fig. 75, _a_), and infraspinatus (Fig. 75,
_c_), and the teres major (Fig. 75, _d_).
_Action._--Draws the scapula toward the vertebral column.
=M. cleidomastoideus= (clavicular portion of the human
sternocleidomastoid) (Fig. 65, _h_).--A narrow flat muscle between the
mastoid process and the clavicle.
_Origin_ from the apex and caudal margin of the mastoid process of the
temporal bone, by tendon and muscle fibres. The muscle passes caudad,
becoming broader and thinner.
_Insertion_ into the lateral four-fifths of the clavicle within the
insertion of the clavotrapezius, and into the raphe which continues
laterad of the clavicle.
_Relations._--Outer or lateral surface at the caudal end with the
clavotrapezius (Fig. 65, _j_); further craniad with the depressor conchæ
(Fig. 64, _b_), the platysma, and the sternomastoid (Fig. 65, _g_).
Inner or medial surface with the supraspinatus (Fig. 75, _a_) caudad,
with the mass of fat in the axilla at its middle, with the levator
claviculæ ventralis (Fig. 65, _i_) and obliquus capitis superior (Fig.
71, _e_) craniad.
_Action._--Pulls the clavicle craniad when the head is fixed. Turns the
head and depresses the snout when the clavicle is fixed.
=M. levator scapulæ ventralis=, or levator claviculæ (Fig. 68, _f_; Fig.
65, _i_; Fig. 72, _c_, _c′_, _c″_) (not usually found in man).
_Origin_ (Fig. 72, _c′_, _c″_) in two parts. (1) By fleshy fibres from
the ventral surface of the atlantal transverse process near its caudal
border (_c′_). (2) By a small tendon from the ventral surface of the
basioccipital opposite the middle of the length of the bulla tympani
(_c″_) in common with the longus capitis (_a_). The two heads unite to
form a flat band which passes caudoventrad and is inserted (Fig. 76,
_f_) by a flat short tendon, about eight millimeters broad, into the
outer surface of the metacromion along its ventral border, and into the
infraspinatus fossa for one or two millimeters distad of that border.
_Relations._--Near the insertion the dorsal border overlaps the border
of the acromiotrapezius (Fig. 68, _h_), and the ventral border is
attached by strong fascia to the border of the clavotrapezius (Fig. 68,
_d_). The outer surface is in relation with the longissimus capitis
(Fig. 73, _g_), clavotrapezius (Fig. 68, _d_), cleidomastoid (Fig. 73,
_d_), platysma, and the skin. The inner surface is in relation caudad
with the supraspinatus and with a mass of fat and a lymphatic gland
which occupy the hollow of the shoulder. Craniad it is in relation with
the cleidomastoid (Fig. 73, _d_), the scalenus (Fig. 73, _f_), the
longus capitis (Fig. 73, _e_), and the obliquus superior (Fig. 71, _e_).
_Action._--Pulls the scapula craniad.
=M. latissimus dorsi= (Fig. 68, _m_; Fig. 65, _q_; Fig. 77, _e_).--A
large triangular sheet covering rather more than the dorsocranial half
of the abdomen and thorax. It arises from the middorsal line, from the
pelvis to the fifth thoracic spine, and is inserted into the humerus.
_Origin_ from the tips of the neural spines of the vertebræ from the
fourth or fifth thoracic to about the sixth lumbar. As far as the tenth
or eleventh thoracic vertebra the origin is directly by muscle-fibres.
Caudad of this is a broad triangular tendon which may be so closely
united to the tendons of the underlying muscles that it cannot be
separated. The muscle passes cranioventrad, the fibres converging to the
axilla. In the axilla a part of the cutaneus maximus and the
epitrochlearis (Fig. 65, _r_) take origin from the outer surface.
_Insertion._--The muscle then ends in a flat tendon, to the cranial
surface of which the fibres of the teres major (Fig. 77, _c_) are
attached. Five to ten millimeters from the humerus the muscle-fibres of
the teres give place to the tendon-fibres, and the conjoined tendon of
the teres and latissimus which is thus formed (Fig. 79, _d′_) is
inserted into a rough elongated area (Fig. 82, _f_) which lies parallel
with the pectoral ridge on the medial surface of the shaft of the
humerus (Fig. 48, _g_). The teres tendon forms the proximal part of the
conjoined tendon. A part of the tendon of the latissimus may join the
pectoralis minor at its distal or caudal border (Fig. 65), and thus it
may contribute to the formation of both pillars of the bicipital arch
(Fig. 65, _t′_).
_Relations._--Its outer surface is covered caudad by the cutaneus
maximus, and craniad by the spinotrapezius (Fig. 68, _j_) and the long
head of the triceps (Fig. 68, _k_). The cranial border comes into
relation with the spinotrapezius (j) and teres major (Fig. 77, _c_).
The caudal border is in contact at the ventral end with the
xiphihumeralis (Fig. 65, _p_) and pectoralis minor (Fig. 65, _o_). The
inner surface of the latissimus covers near its cranioventral end parts
of the xiphihumeralis (Fig. 68, _n_), pectoralis minor (Fig. 68, _o_),
teres major (Fig. 77, _c_), and serratus anterior (Fig. 73, _i_). The
caudal border covers a portion of the obliquus externus abdominis (Fig.
68, _p_); the dorsal and middle portions cover parts of the longissimus
dorsi (Fig. 69, _f″_), the spinalis dorsi (Fig. 69, _g_), the serratus
posterior superior (Fig. 73, _l_), and serratus posterior inferior (Fig.
73, _n_).
_Action._--Pulls the arm caudodorsad.
=M. serratus anterior= and =levator scapulæ= (Fig. 73, _i_ and _h_) in
the cat are continuous at both origin and insertion, and it is barely
possible to separate their contiguous borders without cutting the
fibres. The muscle extends from the transverse processes of the last
five cervical vertebræ and from the first nine or ten ribs to the medial
surface of the scapula near its vertebral margin (Fig. 78, _c_ and _d_).
=M. serratus anterior= (or serratus magnus) (Fig. 73, _i_).
_Origin._--From the first nine or ten ribs in as many subdivisions. The
first subdivision arises from the whole or nearly the whole of the
caudal border of the first rib. The next four or five arise either from
the ribs or from the costal cartilages near or at their junction with
the ribs. The last four subdivisions arise from the ribs at increasing
distances from the cartilages. The fibres converge and the subdivisions
join one another.
_Insertion_ (Fig. 78, _c_) into a narrow area on the medial surface of
the scapula near the vertebral border. The glenoid half of the insertion
is by a short tendon, the remainder by muscle-fibres.
_Relations._--Outer (lateral) surface with the latissimus dorsi (Fig.
68, _m_), teres major (Fig. 77, _c_), subscapularis (Fig. 77, _a_), and
near the origin with the rectus abdominis (Fig. 73, _k_), the scalenus
(Fig. 73, _f_-_f‴_), and the obliquus externus (Fig. 68, _p_). Inner
(medial) surface with the serratus posterior superior (Fig. 73, _l_) and
its tendon, and with the intercostales externi (Fig. 73, _m_). At its
insertion the muscle touches the rhomboideus. The cranial edge is united
to the caudal edge of the levator scapulæ (Fig. 73, _h_).
_Action._--Depressor of the scapula.
=M. levator scapulæ= (Fig. 73, _h_).
_Origin._--From the dorsal tubercles of the transverse processes of the
last five cervical vertebræ and from the ligaments between the
tubercles. A slip sometimes arises from the atlas.
_Insertion_ (Fig. 78, _d_) into a triangular area on the medial surface
of the scapula near its vertebral border. It is continuous with the
insertion of the serratus anterior.
_Relations._--Outer (lateral) surface with a mass of fat separating it
from the clavotrapezius (Fig. 68, _d_) and cleidomastoid (Fig. 65, _h_),
and with the subscapularis (Fig. 77, _a_). Inner (medial) surface with
the splenius (Fig. 73, _b_), the tendon of the serratus posterior
superior (Fig. 73, _l_), and the cervical portion of the longissimus
dorsi (Fig. 69, _f″_). Near the insertion the muscle touches the
occipitoscapularis (Fig. 73, _a_) and rhomboideus. Caudal border united
with the serratus anterior (Fig. 73, _i_).
_Action._--Draws the scapula cranioventrad.
B. MUSCLES OF THE BACK (interconnecting parts of the vertebral column)
(Fig. 69).--The muscles connected with the vertebral column form a mass
which is less markedly differentiated into distinct muscles than is the
case in the limbs. A great longitudinal mass of fibres begins in the
sacral region and extends along the vertebral column to the head. This
mass contains fibres running in various directions and attached at one
or both ends to the sacrum, the innominate bones, the spinous,
transverse, and articular processes, and to the arches, of the vertebræ;
to the ribs and to the head, and having in general the function of
moving the vertebræ in various ways, or of moving parts connected with
the vertebræ. In some regions, especially the cervical, it is possible
to distinguish clearly distinct muscles which have been differentiated
from this mass. In the greater part of its extent, however, it is
possible to distinguish only more or less closely interconnected
bundles,--the more clearly marked of which have received special names.
The great dorsal mass running along each side of the vertebral column,
occupying the space between the spinous processes and the transverse
processes, receives the general name of =M. extensor dorsi communis=;
the separate muscles are to be considered as parts or differentiations
of this. The largest part of the mass is in the lumbar region (first
portion of the =longissimus dorsi=, Fig. 69, _f_). At the caudal end of
the thorax a lateral mass, parts of which become connected with the
ribs, is separated off from the main part of the muscle; this extends
craniad into the cervical region as =M. iliocostalis= (_h_). The main
portion of the longissimus dorsi (_f′_) continues craniad on the medial
side of the iliocostal into the neck region. At about the level of the
eighth or ninth thoracic vertebra a strip begins to become separated off
on the medial side of the longissimus; further forward it becomes
clearly distinct, forming the =spinalis dorsi= (_g_). The separate
muscles connecting the cervical vertebræ with each other and with the
head are differentiations of the extensor dorsi communis.
A still deeper set of fibres, interconnecting the vertebræ, forms the
=multifidus spinæ= and a number of other small muscles.
A description of the different bundles of fibres, under the names
usually given, follows. Certain general principles are observed in some
of the names used. Muscles which interconnect the spinous processes of
the vertebræ receive the name =spinalis.= Those interconnecting
contiguous spinous processes are called =interspinalis.= Muscles
attached at one end to transverse processes, at the other to the spinous
processes, receive the name =transversospinalis=. =Semispinalis= has the
same signification as transversospinalis, but is a name usually
applied to subdivisions of the transversospinalis group. The
=intertransversarii= are muscles interconnecting the transverse
processes.
[Illustration: FIG. 69.--DEEP MUSCLES OF BODY, EXPOSED AFTER REMOVAL
OF THE MUSCLES SHOWN IN FIG. 73.
_a_, M. biventer cervicis; _b_, M. complexus; _c_, M. obliquus capitis
superior; _d_, M. longus atlantis; _e_, cut end of M. longissimus
capitis; _f_, _f′_, _f″_, M. longissimus dorsi; _g_, M. spinalis
dorsi; _h_, M. iliocostalis; _i_, Mm. intercostales externi; _k_, Mm.
intercostales interni; _l_, M. transversus abdominis.]
(_a_) _Muscles of the Lumbar and Thoracic Regions._--The muscles of the
lumbar and thoracic regions are mostly covered by a strong fascia, known
as the =lumbodorsal= fascia (Fig. 68, _y_). This consists of two sheets,
the superficial sheet being applied directly to the outer surface of the
inner sheet, or separated from it by a mass of fat.
The superficial sheet (Fig. 68, _y_) overlies the lumbar region and the
caudal half of the thoracic region. On the medial side it is attached to
the spinous processes of the vertebræ and is united closely to the
deeper layer. Laterally this fascia is continuous with the latissimus
dorsi (_m_) and obliquus abdominis externus (_p_). Caudad it is attached
to the spine of the ilium and becomes continuous with the fascia
covering the gluteus muscles.
The deeper sheet (Fig. 70, _c_) is of a tendinous character, forming the
external tendinous layer of the longissimus dorsi, many of whose fibres
take origin from its under surface. It is described more fully in the
account of this muscle.
=M. longissimus dorsi= (Fig. 69, _f_, _f′_, _f″_; Fig. 70, _a_ and
_b_).--A very large muscle, filling most of the region between the
spinous processes and transverse processes of the lumbar and thoracic
vertebræ, and extending into the cervical region.
The muscle is largest in the lumbar region (Fig. 69, _f_; Fig. 70),
where it is divided into a narrow medial (Fig. 70, _a_) and a thick
lateral portion (Fig. 70, _b_), the latter being again partially
subdivided by the fascia. The two parts unite farther craniad.
The =medial division= (Fig. 70, _a_) consists of muscular bundles
connecting the spinous processes of the vertebræ with the accessory and
mammillary processes of other vertebræ; it is continuous caudad with the
extensor caudæ lateralis (Fig. 70, _f_). The muscle-fibres take origin
in the sacral region by small round tendons from the spinous processes
of the last two sacral and the caudal vertebræ. They curve
cranioventrad, forming a large belly, and are inserted into the
accessory and mammillary processes of the lumbar vertebræ. In the
thoracic region this division unites with that portion of the lateral
division in which the fibres coming from the fascia of origin are
inserted into the laminæ and transverse processes of the thoracic
vertebræ.
The =lateral division= (Fig. 70, _b_) is much larger than the medial
one, forming in the lumbar region a nearly cylindrical mass.
[Illustration: FIG. 70.--MUSCLES ON THE DORSAL SIDE OF THE VERTEBRAL
COLUMN IN THE LUMBAR, SACRAL, AND CAUDAL REGIONS.
Both sheets of the lumbodorsal fascia have been removed, the deep
layer (_c_) being cut where it passes into the longissimus dorsi. 1,
crest of ilium; 4-7, tips of spinous processes of the fourth to
seventh lumbar vertebræ. _I_, _II_, tips of spinous processes of first
two sacral vertebræ. _a_, _b_, M. longissimi dorsi (_a_, medial
portion; _b_, lateral portion; _b′_, portion taking origin from the
lumbodorsal fascia); _c_, cut edge of deep layer of lumbodorsal
fascia; _d_, M. multifidus spinæ; _e_, M. extensor caudæ medialis;
_f_, M. extensor caudæ lateralis, _g_, M. abductor caudæ externus.]
_Origin_ from the crest of the ilium (Fig. 70, 1) and the medial surface
of the ilium as far caudad as the auricular impression; also from the
deep layer of the lumbodorsal fascia (_c_). This fascia is connected
with the crest of the ilium and with the tips of the spinous processes
of the vertebræ in the lumbar and thoracic regions, and from it a large
proportion of the fibres of the longissimus take origin. In the lumbar
region it dips into the muscle as an intermediate longitudinal sheet
(_c_), partially dividing it lengthwise into two parts. Fibres taking
origin from the lateral surface of this intermediate sheet curve
cranioventrad, and are inserted on the transverse processes of the
lumbar vertebræ. Fibres taking origin from the medial surface of the
sheet pass mediocraniad and are inserted into the accessory processes
and the surfaces of the vertebral arches. In the thoracic region (Fig.
69, _f′_) most of the fibres are inserted in separate bundles by small
tendons on the transverse processes of the vertebræ, while some of the
medial fibres unite with tendinous strands which become attached to the
laminæ and articular processes of the vertebræ. At the region of the
eighth or ninth thoracic vertebra the =spinalis dorsi= (Fig. 69, _g_)
begins to be separated off on the medial side, the separation becoming
complete only some distance farther craniad; the longissimus dorsi then
continues into the cervical region (_f″_). Bundles of fibres become
attached in the manner above described to transverse processes of all
the thoracic vertebræ. In the cervical region (_f″_) the muscle spreads
out and becomes thinner, and bundles of fibres become attached to the
transverse processes of the cervical vertebræ as far forward as the
second. In the more cranial portion of its extent the muscle receives
fibres having origin on the articular processes and laminæ of the
cervical and a few of the more cranial thoracic vertebræ.
The portion of the muscle which is inserted on the cervical transverse
processes (_f″_) is sometimes distinguished as the =longissimus
cervicis=; it is not well separated from the rest of the muscle in the
cat. The =longissimus capitis= (Fig. 69, _c_; Fig. 73, _g_) is to be
considered a differentiated cranial portion of this muscle.
_Relations._--Outer surface with the following, beginning with the
caudal end: the sartorius (Fig. 68, _q_), the latissimus dorsi (Fig. 68,
_m_), the lumbodorsal fascia (Fig. 68, _y_), the serratus posterior
inferior (Fig. 73, _n_) and superior (Fig. 73, _l_), and the levator
scapulæ (Fig. 73, _h_). Lateral margin with the abdominal muscles, the
iliocostal (Fig. 69, _h_), and the levator scapulæ (Fig. 73, _h_).
Medial side with the multifidus spinæ (Fig. 70, _d_), the spinous
processes of the thoracic vertebræ, the spinalis dorsi (Fig. 69, _g_),
the complexus (Fig. 69, _b_), the biventer cervicis (Fig. 69, _a_), and
the longissimus capitis (Fig. 69, _e_).
_Action._--Extends the vertebral column.
=M. iliocostalis= (Fig. 69, _h_).--This is a muscle about 1½ to 2
centimeters wide, lying on the dorsal portion of the ribs, laterad of
the longissimus dorsi (_f′_). It is composed of many partly separated
bundles, each with an oblique tendon. The muscle begins at the last or
next to the last rib, where it is connected with the longissimus by a
rather small bundle of fibres. The rest of the muscle-fibres take origin
in bundles from the lateral surface of the ribs, at about the angles, or
from thin tendons connecting the angles, of the ribs; they pass
obliquely craniad and are inserted, usually by tendons, on the lateral
surface of the third or fourth rib craniad of the one on which the given
bundle has origin. The insertions on any given rib lie ventrad of the
origins on the same rib. In the cat this muscle is confined to the
thoracic region.
_Relations._--Outer surface with the serratus posterior inferior (Fig.
73, _n_) and superior (Fig. 73, _l_), and the levator scapulæ (Fig. 73,
_h_). Inner surface with the dorsal surface of the ribs, the external
intercostals (Fig. 69, _i_), and craniad with the levatores costarum.
Medial edge in contact with the longissimus dorsi (Fig. 69, _f′_).
_Action._--Draws the ribs together.
=M. spinalis dorsi= (Fig. 69, _g_).--A muscle interconnecting the
spinous processes of vertebræ some distance apart, in the thoracic and
cervical regions. It lies on the medial side of the longissimus dorsi
(_f′_).
_Origin_ by strong tendons from the tips of the spinous processes of the
tenth to the thirteenth thoracic vertebræ. These tendons represent the
cranial portion of the deep layer of the lumbodorsal fascia, and give
origin also to many fibres of the longissimus dorsi, so that the two
muscles are completely united at the origin of the spinalis. They become
separated at about the level of the sixth thoracic vertebra, the
spinalis forming a strong separate bundle passing into the neck region
close against the sides of the spinous processes. The insertion is by
fleshy bundles into the sides of the spinous processes of the first nine
or ten thoracic vertebræ and of the cervical vertebræ as far forward as
the second. Some of the fibres of this muscle pass craniad into the
biventer cervicis (Fig. 69, _a_).
_Relations._--Outer surface with the tendons of the serratus posterior
inferior (Fig. 73, _n_) and serratus posterior superior (Fig. 73, _l_),
and with the splenius (Fig. 73, _b_), biventer cervicis (Fig. 69, _a_),
and complexus (Fig. 69, _b_). Lateral and ventral surface with the
longissimus dorsi (_f′_); medial surface with the spinous processes and
the multifidus spinæ.
_Action._--Extensor of the vertebral column.
=M. multifidus spinæ=.--This consists of bundles of fibres which have
origin on the transverse processes or neighboring parts, pass
craniodorsad across one or more vertebræ, and are inserted into the
spinous processes of vertebræ lying some distance craniad of the origin.
They lie deeper than the muscles previously described. The muscle is
most strongly developed in the lumbar region (Fig. 70, _d_), where it
forms a thick interwoven mass in which it is difficult to distinguish
separate bundles. The fibres in this region have origin on the accessory
or mammillary processes and usually pass over more than one vertebra
between origin and insertion; their insertions reach the dorsal ends of
the spinous processes, so that part of the muscle lies immediately
beneath the lumbar fascia. In other regions the multifidus is covered by
other muscles. In the thoracic region the separate bands are more
distinct, and usually pass in their course over but one intervening
vertebra. In the cervical region the bands are interconnected, forming a
fairly distinct single muscle, which is described separately below as
the =semispinalis cervicis= (Fig. 71, _c_). The portion of this muscle
attached to the head (=semispinalis capitis=) forms the biventer
cervicis (Fig. 69, _a_) and complexus (_b_). Caudad this muscle passes
onto the tail as the =extensor caudæ medialis= (Fig. 70, _c_).
_Relations._--Outer and lateral surface in the lumbar region with the
longissimus dorsi (Fig. 69, _f_) and the lumbodorsal fascia (Fig. 68,
_y_); in the thoracic region with the longissimus dorsi (Fig. 69, _f′_)
and spinalis dorsi (_g_). Inner surface with the arches, articular
processes, and spinous processes of the vertebræ.
_Action._--Extends the back when the muscles of both sides work
together. Turns the vertebral column obliquely sideways when one set
acts alone.
The deepest layer of the multifidus forms what is sometimes
distinguished as the =Mm. rotatores=; no separate layer of this sort is
to be made out in the cat.
=Mm. interspinales.=--Muscle-bundles passing from the spinous process of
one vertebra to that of the vertebra immediately craniad or caudad of
it. They are best developed in the lumbar region.
=Mm. intertransversarii.=--Muscle-fibres interconnecting the transverse
processes. In the lumbar region the =intertransversarii mediales=
connect the accessory and mammillary processes; the =intertransversarii
laterales= lying between the transverse processes. In other regions only
one set of the intertransversarii is to be distinguished.
(_b_) _Dorsal Muscles of the Cervical Region._--The clavotrapezius (Fig.
68, _d_) and occipitoscapularis (Fig. 73, _a_) have been described in
connection with the muscles of the shoulder. The remaining muscles of
this region may be considered as differentiations of the general
vertebral musculature (M. extensor dorsi communis).
=M. splenius= (Fig. 73, _b_.)--A large sheet of muscle covering the
dorsal part of the side of the neck, beneath the trapezii.
_Origin_ from the whole cervical ligament and from the fascia covering
the deeper muscles along a line which extends from the first thoracic
spinous process caudolaterad for about two centimeters.
_Insertion_ by a thin tendon into the whole lambdoidal ridge. Laterad
the tendon may be fused with that of the longissimus capitis (Fig. 73,
_g_).
_Relations._--Outer surface with the sternomastoid (Fig. 68, _c_),
occipitoscapularis (Fig. 73, _a_), clavotrapezius (Fig. 68, _d_),
rhomboideus, tendon of the serratus posterior superior (Fig. 73, _l_),
and the levator scapulæ (Fig. 73, _h_). Lateral edge closely united with
the longissimus capitis (Fig. 73, _g_). Inner surface with the
longissimus capitis, complexus (Fig. 69, _b_), and biventer cervicis
(Fig. 69, _a_).
_Action._--Lateral flexor of the head. The two together elevate the
head.
=M. longissimus capitis= (=trachelomastoideus=) (Fig. 73, _g_; Fig. 69,
_e_).--This is a slender muscle lying close against the lateral border
of the splenius (Fig. 73, _b_), and sometimes fused with the splenius at
its craniad end. It is a cranial continuation of the longissimus dorsi
(Fig. 69, _f″_).
_Origin_ by five slips which are attached by strong tendons to the
anterior articular processes of the last four cervical vertebræ. The
tendons are common to this muscle and the complexus. The five slips
unite to form a flat belly which has its
_Insertion_ by a strong rounded tendon into the mastoid process of the
temporal bone. The tendon may be closely united to that of the splenius.
_Relations._--Lateral surface with the sternomastoid (Fig. 68, _c_), the
levator scapulæ (Fig. 73, _h_), and longissimus dorsi (Fig. 69, _f″_).
Medial surface with the splenius (Fig. 73, _b_) (to which it is partly
united), the complexus (Fig. 69, _b_), and the longus atlantis (Fig. 69,
_d_).
_Action._--Lateral flexor of the head.
=M. biventer cervicis= (Fig. 69, _a_) (=medial portion of M.
semispinalis cervicis et capitis=).--The biventer cervicis is a flat
muscle which lies beneath the splenius (Fig. 73, _b_), next the median
line of the neck, with its fibres longitudinal.
_Origin_ in three or four slips from the surface of the three or four
aponeurotic arches which take origin from the tips of the spinous
processes of the last cervical and the first three thoracic vertebræ and
pass laterad and caudad to the anterior processes of the second, third,
fourth, and fifth thoracic vertebræ. These arches are deviated from
their straight course by four aponeurotic bands which pass from them
obliquely caudad and dorsad to the sides of the spinous processes of the
vertebræ into which the arches are inserted. The arches form the
beginning of the sheet of fascia which passes outside of the
longitudinal supraspinous muscles, and the anchoring bands form the
beginning of a similar sheet which passes within the longitudinal
supraspinous muscles. An additional slip may take origin from the
cervical ligament between the last cervical and the first thoracic
vertebræ. The fibres form a flat band divided by two or three oblique
tendinous intersections. It adheres closely to the cervical supraspinous
ligament.
_Insertion_ by a strong tendon into the medial part of the lambdoidal
crest.
_Relations._--Outer surface with the splenius (Fig. 73, _b_) and at the
caudal end with the longissimus dorsi (Fig. 69, _f″_). Inner surface
with the spinalis dorsi (Fig. 69, _g_), the semispinalis cervicis (Fig.
71, _c_), and the rectus capitis posterior major (Fig. 71, _a_). Medial
edge with the muscle of the opposite side; lateral edge with the
complexus (Fig. 69, _b_).
_Action._--Raises the snout.
=M. complexus= (Fig. 69, _b_) (=lateral portion of M. semispinalis
cervicis et capitis=).--The complexus is closely associated with the
biventer cervicis (_a_) and lies on its lateral side beneath the
splenius (Fig. 73, _b_).
_Origin_ by tendinous bands from the anterior articular processes of the
last five or six cervical and the first one, two, or three thoracic
vertebræ. The same bands give origin externally to the fibres of the
longissimus capitis (Fig. 69, _e_), and internally to those of deeper
muscles of the neck. The six or more muscular slips continued from these
tendons unite to form a flat band, the
_Insertion_ of which is by a flat tendon into the medial third of the
lambdoidal crest some distance ventrad of the free edge of the crest.
Near the insertion the lateral border of the muscle is connected by an
aponeurotic band to the lateral border of the transverse process of the
atlas.
_Relations._--Outer surface at the dorsal border with the biventer
cervicis (Fig. 69, _a_); at the middle with the splenius (Fig. 73, _b_);
at the ventral border with the longissimus capitis (Fig. 69, _e_) and
the longissimus dorsi (Fig. 69, _f″_). Inner surface with the cervical
portion of the spinalis dorsi, with the semispinalis cervicis (Fig. 71,
_c_), the obliquus capitis inferior (Fig. 71, _b_), the rectus capitis
posterior major (Fig. 71, _a_), and the obliquus superior (Fig. 71,
_e_).
_Action._--Raises the head.
=M. spinalis dorsi= extends into the cervical region; it has been
described.
=M. semispinalis cervicis= (Fig. 71, _c_).--This represents that portion
of the multifidus spinæ which extends into the cervical region. It is
not composed of distinct bundles, like the multifidus of the thoracic
region, but all the fibres are united into a fairly well-defined muscle.
_Origin_ from the articular processes of the last five cervical
vertebræ.
_Insertion_ into the spinous processes of the cervical vertebræ up to
the second, the largest part of the muscle being inserted into the
caudal end of the spine of the atlas.
_Relations._--Outer surface with the spinalis dorsi (Fig. 69, _g_) and
the complexus (Fig. 69, _b_). Inner surface with the vertebræ.
_Action._--Extends the neck.
=M. longissimus dorsi= extends into the cervical region, where it is
often distinguished as the =longissimus cervicis= (Fig. 69, _f″_). It
has been described.
=M. longus atlantis= (Fig. 71, _f_; Fig. 69, _d_).--This represents a
differentiated portion of the longissimus dorsi.
_Origin_ from the transverse process and the side of the vertebral arch
of the third cervical vertebra.
_Insertion_ into the caudolateral angle of the wing of the atlas.
_Relations._--Dorsal surface with the complexus (Fig. 69, _b_), the
longissimus capitis (Fig. 69, _e_), and the obliquus inferior (Fig. 71,
_b_). Ventral surface with the scalenus (Fig. 71, _g_), longissimus
dorsi (Fig. 69, _f″_), and levator scapulæ (Fig. 71, _h_).
_Action._--Extends the neck and turns the head sideways.
=M. rectus capitis posterior major= (Fig. 71, _a_).
_Origin._--The whole length of the spinous process (or crest) of the
axis, or its caudal part only. It is united by a raphe to the opposite
muscle. The muscle passes craniad and laterad to its
_Insertion_ into an area ventrad of the medial part of the lambdoidal
crest beneath the insertion of the complexus (Fig. 69, _b_) and the
biventer cervicis (Fig. 69, _a_).
_Relations._--Dorsal surface with the biventer cervicis (Fig. 69, _a_).
Ventral surface with the rectus capitis posterior medius (Fig. 71, _d_)
and the obliquus capitis inferior.
_Action._--Raises the snout.
=M. rectus capitis posterior medius= (Fig. 71, _d_). (This is in man a
part of the rectus capitis posterior major.)--It lies beneath the rectus
capitis posterior major (Fig. 71, _a_).
[Illustration: FIG. 71.--DEEP MUSCLES OF THE NECK, AFTER THE REMOVAL
OF MM. BIVENTER CERVICIS AND COMPLEXUS.
_a_, M. rectus capitis posterior major; _b_, M. obliquus capitis
inferior; _c_, M. semispinalis cervicis; _d_, M. rectus capitis
posterior medius; _e_, M. obliquus capitis superior; _f_, M. longus
atlantis; _g_, M. scalenus (part of cervical portion); _h_, cut end of
M. levator scapulæ.]
_Origin_ from the cranial end of the axial spine. It forms a triangular
prismatic mass which passes craniad and has its
_Insertion_ into an elongated area on the occipital bone, ventrad of the
median half of the lambdoidal crest.
_Relations._--Dorsal surface with the rectus capitis posterior major
(Fig. 71, _a_). Ventral surface with the atlas and the rectus capitis
posterior minor.
_Action._--Assists the rectus capitis posterior major.
=M. rectus capitis posterior minor.=--A small triangular muscle beneath
the rectus capitis posterior medius (Fig. 71, _d_).
_Origin_ by the apex of the triangle from the cranial border of the
dorsal arch of the atlas for about two millimeters laterad of the median
line. The muscle passes over the ligament which connects the atlas to
the occiput and adheres to it.
_Insertion_ into an elongated area on the occipital bone, ventrad of the
insertion of the rectus capitis posterior medius for about five
millimeters next to the median line.
_Relations._--Dorsal surface with the rectus capitis posterior medius.
Ventral surface with the posterior atlanto-occipital membrane.
_Action._--Assists the rectus capitis posterior major.
=M. obliquus inferior= (Fig. 71, _b_).
_Origin_ from the whole lateral surface of the spine of the axis. The
parallel fibres form a thick mass which passes laterad and craniad.
_Insertion_ into the dorsal surface of the transverse process of the
atlas along a narrow area near its lateral margin.
_Relations._--Outer surface with the rectus capitis posterior major
(Fig. 71, _a_), the complexus (Fig. 69, _b_), and the obliquus superior
(Fig. 71, _e_). Inner surface with the axis.
_Action._--Rotates the head.
=M. obliquus capitis superior= (Fig. 71, _e_; Fig. 72, _e_).--This is a
triangular muscle passing from the outer border of the atlas laterad of
the recti capitis posteriores to the occiput.
_Origin_ from the lateral border of the transverse process of the atlas
on its ventral margin. The fibres pass craniad and diverge.
_Insertion_ into the caudal side of the mastoid process of the temporal
bone and into a line parallel with the lambdoidal ridge and ventrad of
it, from the mastoid process to within one centimeter of the median
line.
_Relations._--Outer surface with the splenius (Fig. 73, _b_), complexus
(Fig. 69, _b_), and longissimus capitis (Fig. 73, _g_). Inner surface
with the obliquus inferior (Fig. 71, _b_), the wing of the atlas, and
the rectus lateralis (Fig. 72, _d_). Ventral border with the
cleidomastoid (Fig. 73, _d_) and one head of the levator scapulæ
ventralis (Fig. 72, _c′_).
_Action._--Flexes the head laterally.
=Mm. interspinales= and =intertransversarii= are found in the neck
region also; they are described with the muscles of the back.
C. MUSCLES OF THE TAIL.--=M. extensor caudæ medialis= (Fig. 70,
_e_).--This is a continuation caudad of the multifidus spinæ (Fig. 70,
_d_); it lies next to the dorsal median line, the muscles of right and
left side touching one another in the middle line.
_Origin_ by numerous fleshy bundles from the spinous processes of the
sacral and first caudal vertebræ. The fibres pass caudad and are
inserted by tendons into the articular processes and the dorsal surface
of the caudal vertebræ.
_Action._--Extends (raises) the tail.
=M. extensor caudæ lateralis= (Fig. 70, _f_).--This is a continuation
caudad of the medial portion of the longissimus dorsi (Fig. 70, _a_); it
lies just laterad of the extensor caudæ medialis (Fig. 70, _e_).
_Origin_ in many fleshy bundles from the articular processes of the
sacral vertebræ, and the transverse processes of the caudal vertebræ.
The fibres curve dorsocaudad and are inserted by many long slender
tendons on the dorsal surfaces of the caudal vertebræ. The muscle grows
continually smaller as it passes caudad.
_Action._--Raises the tail.
=M. abductor caudæ= (coccygis) =externus= (Fig. 68, _w_; Fig. 70,
_g_).--A rounded muscle on the lateral surface of the cranial part of
the tail.
_Origin_ from the medial side of the dorsal border of the ilium, and
from the dorsal surface of the sacrum. The muscle passes caudad, lying
just ventrad of the extensor lateralis, and is _inserted_ into the
transverse processes and lateral surfaces of the caudal vertebræ, as far
back as the eighth or ninth.
_Action._--Bends the tail sideways.
=M. abductor caudæ internus= (or M. coccygeus).--A large flat muscle,
having origin on the spine of the ischium. The muscle passes
dorsomediad, spreading out, and is inserted into the transverse
processes of the second to the fourth caudal vertebræ.
_Relations._--Lateral surface with the caudofemoralis (Fig. 68, _s_),
gluteus maximus, and pyriformis. Medial surface with the iliocaudalis
and the flexor caudæ longus (Fig. 68, _x_).
=M. iliocaudalis= (Str.-D.) (Fig. 162, 11′, page 398).--This represents
a portion of the levator ani of man, and in some specimens is united
with that muscle (Fig. 162, 11) in the cat.
_Origin_ along the ventral half of the medial surface of the ilium,
caudad of the sacrum. The fibres pass caudad and are _inserted_ by a
flat tendon into the ventral surface of the caudal vertebræ, from the
second or third to about the seventh.
_Relations._--Lateral surface with the gluteus maximus and abductor
caudæ internus (Fig. 68, _w_). Medial surface with the levator ani (Fig.
162, 11), with which this muscle may be partly united.
_Action._--The two muscles together flex the tail.
=M. flexor caudæ longus= (Fig. 162, 12; Fig. 113, _c_, page 270).
_Origin_ on the ventral surface of the last lumbar vertebra, of the
sacrum, and of the transverse processes of the caudal vertebræ. Caudad
the muscle forms long, strong tendons which are _inserted_ on the
ventral surface of the tail.
_Relations._--Lateral surface with the ilium, the gluteus maximus, the
abductor caudæ internus, the iliocaudalis, and the skin of the tail.
Dorsally it touches in the caudal region the abductor caudæ externus
(Fig. 68, _w_), medially the flexor caudæ brevis (Fig. 162, 13).
_Action._--Flexes the tail.
=M. flexor caudæ brevis= (Fig. 162, 13).
_Origin_ on the ventral surface of the caudal vertebræ, from the first
to the seventh or eighth. The principal head comes from the first
vertebra. The bundles thus formed pass caudad and are inserted each into
the ventral surface of a vertebra some distance caudad of the origin.
The muscle extends to about the tenth caudal vertebra, and its most
caudal parts are closely interconnected with the flexor caudæ longus.
_Relations._--Lateral edge with the flexor caudæ longus. Medial edge in
the sacral region with the levator ani (Fig. 162, 11) and the
iliocaudalis (Fig. 162, 11′); in the caudal region with the muscle of
the opposite side.
_Action._--Flexes the tail.