A. LUMBAR AND THORACIC REGIONS.--The iliopsoas (Fig. 162, 8) belongs in
this group, but since it moves the leg it is described with the muscles
of the pelvic limbs.
=M. psoas minor= (Fig. 162, 9, page 398).--This muscle lies along the
ventral surface of the vertebral column, next to the peritoneum, and
extends from the thoracic vertebræ to the ilium.
_Origin_ usually by five heads, from the caudal border of the centra of
the last two (or one) thoracic and first three (or four) lumbar
vertebræ. These heads also serve as origin for a part of the iliopsoas,
and are closely united at their origin with the quadratus lumborum. They
unite to form an, at first, rather large flat muscle, which rapidly
becomes smaller caudad, finally forming a slender tendon which is
_inserted_ on the iliopectineal line, just craniad of the acetabulum.
_Relations._--Dorsolateral surface with the quadratus lumborum and
iliopsoas (Fig. 162, 8). Ventral surface with the pleura and diaphragm
near the origin; with the peritoneum caudad.
_Action._--Flexes the back in the lumbar region.
=M. quadratus lumborum.=--A flat muscle lying on the ventral surface of
the transverse processes of the lumbar vertebræ. Craniad it has origin
on the ventral surface of the last two thoracic vertebræ, and by a few
fibres from the last rib. The muscle passes caudad, lying on the lateral
side of the psoas minor (Fig. 162, 9), and becomes attached to each of
the transverse processes of the lumbar vertebræ. Caudad the muscle
passes into a strong flat tendon which is inserted into the anterior
inferior spine of the ilium.
_Relations._--Dorsal surface with the transverse processes and the
intertransverse muscles. Ventral and medial surfaces with the psoas
minor (Fig. 162, 9) and iliopsoas (Fig. 162, 8).
_Action._--Bends the vertebral column sideways.
B. MUSCLES ON THE VENTRAL SIDE OF THE NECK (Fig. 65, page 109).--=M.
sternomastoideus= (Fig. 65, _g_; Fig. 68, _c_).--The sternomastoid
(sternal portion of the human sternocleidomastoid) is a flat band one to
three centimeters wide extending from the cranial end of the manubrium
and the midventral line craniad of it to the lambdoidal ridge.
The _origin_ extends from the cranial end of the manubrium along the
midventral line as far as the caudal border of the cricoid cartilage,
and is in two parts. The =caudal= portion arises from the lateral
surface of the manubrium along the dorsal half of its cranial end, and
from the median raphe for about one centimeter craniad of the manubrium.
Its fibres are parallel and tend to diverge into two layers. The
=cranial= portion arises by means of fibres which cover the median line
and interdigitate with the fibres of the opposite muscle between the
cricoid cartilage and a point a few millimeters craniad of the
manubrium. Its caudal border is thus overlaid by the caudal portion. Its
fibres converge and join those of the caudal portion. The muscle passes
dorsocraniad and is
_Inserted_ by means of a flat tendon into the lateral half of the
lambdoidal ridge and into a continuation of the ridge onto the mastoid
portion of the temporal bone as far as the mastoid process. The thickest
part of the tendon is inserted into the mastoid process.
_Relations._--Outer surface at the caudal end with the pectoralis major
(Fig. 65, _l_); in the middle part with the platysma, the depressor
conchæ (Fig. 64, _b_), and with the external jugular vein (Fig. 65, 5),
which crosses it obliquely; at the cranial end with the submaxillary
(Fig. 65, 2) and parotid (1) glands. Inner surface with the sternohyoid
(Fig. 65, _e_), sternothyroid (_g′_), internal jugular vein, longus
capitis muscle, the cleidomastoid (_h_), levator scapulæ ventralis
(_i_), a large lymphatic gland ventrad of the ear, and the splenius
(Fig. 73, _b_).
_Action._--One muscle turns the head and depresses the snout. Both
together depress the snout.
=M. sternohyoideus= (Fig. 65, _e_).--A slender muscle on the midventral
line of the neck close to the opposite muscle.
_Origin_ from the cranial border of the first costal cartilage. The
muscle passes craniad closely united near its caudal end to the
sternothyroid (_g′_).
_Insertion_ (Fig. 67, _m_) into the outer half of the ventral surface of
the body of the hyoid bone caudad of the origin of the geniohyoid (Fig.
67, _g_).
_Relations._--Outer surface with the sternomastoid (Fig. 65, _g_). Inner
surface with the thyrohyoid (Fig. 65, _f_; Fig. 67, _p_), the trachea
(Fig. 67, 4), and the larynx.
_Action._--Draws the hyoid caudad. Raises the ribs and sternum when the
hyoid is fixed.
=M. sternothyreoideus= (Fig. 65, _g′_).--The sternothyroid lies beneath
the sternohyoid and is connected with it at its caudal end.
_Origin_ from the first costal cartilage beneath the sternohyoid.
_Insertion_ (Fig. 67, _o_) into the lateral part of the caudal border of
the thyroid cartilage of the larynx.
_Relations._--Outer surface with the sternohyoid (Fig. 65, _e_) and
laterally with the sternomastoid (Fig. 65, _g_). Inner surface with the
trachea (Fig. 67, 4), and at the lateral edge with the thyroid gland
(Fig. 67, 6).
_Action._--Pulls the larynx caudad.
=M. scalenus= (Fig. 73, _f_-_f‴_).--This is a large and complex muscle
lying on the ventral side of the neck and the lateral surface of the
thorax. It might equally well be classified with the muscles of the
thorax. It is divisible into a considerable number of interconnected
bundles which are sometimes described as separate muscles.
The largest, middle portion (=scalenus medius=) (_f′_) takes origin by
thin tendons from the sixth, seventh, eighth, and ninth ribs, just
dorsad of their junction with the cartilages; these tendons unite near
their origins to form a flat band which becomes fleshy at about the
fifth rib, passes craniad, and unites just craniad of the first rib with
the other parts of the muscle. The dorsal portion (=scalenus posterior=)
(_f″_) has origin by a very slender tendon from about the middle of the
outer surface of the third or fourth rib; it extends craniad as a narrow
band which passes laterad between the heads of the serratus anterior
(_i_) that are attached to the second and third (or third and fourth)
ribs, and unites with the other heads. The ventral head (part of
=scalenus anterior=) (_f‴_) arises by one or two minute tendons from the
cartilages of the second and third ribs; they are partly united with the
transversus costarum (_j_). This ventral head passes craniad and unites
with the other heads.
These three divisions unite just craniad of the first rib with each
other and with the cervical portion of the muscle (_f_) (part of
=scalenus anterior=). This consists of a number of small bundles of
fibres which arise from the first rib and the transverse processes of
the first thoracic and the last six cervical vertebræ.
The _insertion_ is onto the transverse processes of all the cervical
vertebræ, including the axis and atlas. According to Strauss-Durckheim
the fibres from any given transverse process are inserted into the
transverse processes of all the vertebræ craniad of it.
The muscle is partly continuous craniad with the longus capitis (_e_).
The cervical nerves pass out between the bundles of the cervical
portion.
_Relations._--Outer (lateral) surface in the thoracic region with the
external oblique (Fig. 68, _p_), the pectoralis minor (Fig. 65, _o_),
and in part with the serratus anterior (Fig. 73, _i_); in the cervical
region with the sternomastoid (Fig. 65, _g_). Inner (medial) surface
with the serratus anterior (Fig. 73, _i_), the levator scapulæ (Fig. 73,
_h_), the longus atlantis, the transverse processes of the cervical
vertebræ, and the longus capitis (Fig. 73, _e_).
_Action._--Flexes the neck and draws the ribs craniad.
=M. longus capitis= (or =rectus capitis anterior major=) (Fig. 72, _a_;
Fig. 73, _e_).--This is a long muscle lying on the ventral aspect of the
cervical vertebræ. With the muscle of the opposite side and the
underlying longus colli (Fig. 72, _g′_) it forms a trough in which lie
the œsophagus, pharynx, and trachea.
_Origin_ by five (or six) heads from the ventral margins of the
transverse processes of the cervical vertebræ from the second to the
sixth inclusive. The heads unite into a common belly, the lateral border
of which is united with the levator scapulæ ventralis (Fig. 72, _c_)
near its insertion.
_Insertion_ into the body of the sphenoid bone between the bulla and the
middle line. The insertion extends craniad onto the basisphenoid.
_Relations._--Ventral surface with the sternomastoid (Fig. 65, _g_) and
the large lymphatic gland ventrad of the external ear. Lateral surface
with the scalenus (Fig. 72, _h_) and craniad with the levator scapulæ
ventralis (Fig. 72, _c_-_c″_). Medial surface with the carotid artery,
the trachea, œsophagus, and pharynx. Dorsal edge with the vertebræ, the
longus colli (Fig. 72, _g′_), and the rectus capitis anterior minor
(Fig. 72, _b_).
_Action._--Lowers the snout.
=M. rectus capitis anterior minor= (Fig. 72, _b_).--This is a flat band
beneath (dorsad of) the longus capitis (_a_).
_Origin_ from the ventral surface of the inferior arch (body) of the
atlas (3) for about five millimeters laterad of the middle line.
_Insertion_ into a deep depression on the basioccipital caudad of the
insertion of the longus capitis (_a_) and between the caudal end of the
bulla (1) and the median line.
_Relations._--Ventral surface with the longus capitis (_a_). Dorsal
surface with the anterior (ventral) atlanto-occipital membrane (2).
_Action._--Depresses the snout.
[Illustration: FIG. 72.--MUSCLES ON THE VENTRAL SURFACE OF THE
CERVICAL VERTEBRÆ.
On the left side the longus capitis and one head of the levator
scapulæ ventralis have been cut, in order to show the rectus capitis
anterior minor. _a_, M. longus capitis; _b_, M. rectus capitis
anterior minor; _c_, M. levator scapulæ ventralis (_c′_, its atlantal
head; _c″_, its occipital head); _d_, M. rectus capitis lateralis;
_e_, M. obliquus capitis superior; _f_, M. longissimus capitis; _g_,
M. longus colli (_g′_, its cervical portion; _g″_, its thoracic
portion); _h_, part of M. scalenus. 1, bulla tympani; 2, ventral
atlanto-occipital membrane; 3, ventral arch of atlas; 4, first rib.]
=M. rectus capitis lateralis= (Fig. 72, _d_).--This lies ventrad of the
obliquus superior (_e_) on the ventral face of the transverse process of
the atlas and at first appears to be a part of the obliquus superior.
_Origin_ from the median half of the ventral surface of the transverse
process of the atlas. The fibres form a cylindrical mass which passes
craniad and slightly laterad.
_Insertion_ into the fossa laterad of the condyle of the occipital bone.
_Relations._--Ventral surface with the digastric (Fig. 65, _b_) and the
lymphatic gland ventrad of the ear. Dorsal surface with the wing of the
atlas.
_Action._--Flexes the head laterally.
=M. longus colli= (Fig. 65, _g′_, _g″_).--A long, rather slender muscle
lying on the ventral surface of the cervical and first six thoracic
vertebræ. It consists of many separate bundles, and is divisible into a
thoracic and a cervical portion.
The =thoracic portion= (_g″_) has origin by six heads from the ventral
surface of the first six thoracic vertebræ. The separate heads join to
form a band which passes craniad and is inserted for the most part into
the processus costarius of the sixth cervical vertebra; a portion of it
joins the cervical division of the muscle.
The =cervical portion= (_g′_) is a continuation craniad of the thoracic
portion. It arises in small bundles from the transverse processes and
sides of the ventral surfaces of the centra of the cervical vertebræ.
These bundles pass craniomediad, so that those from the muscles of
opposite sides meet and are inserted on the centra of the vertebræ in
the middle line, each pair of bundles forming a V opening caudad. The
most cranial insertion is into the tubercle on the middle of the ventral
surface of the ventral arch of the atlas (3).
_Relations._--Dorsal surface with the centra of the vertebræ. Ventral
surface in the thorax with the trachea; in the neck with the œsophagus.
Medial edge with the muscle of the opposite side. Lateral margin in the
cervical region with the longus capitis (_a_).
_Action._--Bends the neck.