The ninth, fifteenth, and eighteenth ribs are retained. _a_,
Pericardium; _b_, posterior vena cava; _c_, vena azygos; _c′_,
œsophageal vein; _d_, _e_, anterior vena cava; _f_, brachial vein;
_g_, inferior cervical vein; _h_, jugular vein; _i_, vertebral vein;
_k_, superior cervical vein; _l_, dorsal vein; _m_, trachea; _n_,
root of right lung; _o_, œsophagus; _p_, mediastinal lobe of right
lung; _q_, mediastinum; _r_, bronchial lymph glands; _s_,
mediastinal lymph glands; _t_, costal part of diaphragm; _t′_,
tendinous center of same; _u_, intercostal muscle; _v_, longus
colli; _w_, posterior deep pectoral muscle; _w′_, anterior deep
pectoral muscle; _x_, superficial pectoral muscle; _y_,
sterno-cephalicus; _z_, scalenus; _1_, _5_, right brachial artery;
_2_, dorso-cervical trunk; _2′_, superior or deep cervical artery;
_3_, dorsal artery (cut); _3′_, subcostal artery; _4_, internal
thoracic artery; _6_, external thoracic artery; _7_, inferior
cervical artery; _8_, bicarotid trunk; _10_, aorta; _11_, œsophageal
artery; _12_, thoracic duct; _13_, right phrenic nerve; _14_,
brachial plexus; _15_, right vagus; _15′_, _15″_, œsophageal
continuations of vagi; _16_, right recurrent nerve; _17_, cervical
trunk of sympathetic; _18_, thoracic trunk of sympathetic; _20_,
inferior cervical ganglion; _21_, first thoracic ganglion of
sympathetic; _22_, right cardiac nerve; _23_, longissimus; _24_,
transversalis costarum; _25_, spinalis; _26_, multifidus; _27_,
ligamentum nuchæ. (After Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
The left dorsal artery sometimes arises with the superior cervical by
a common trunk. On the right side there may be a common stem for the
dorsal, superior cervical, and vertebral arteries. Occasionally the
artery arises from the anterior aorta. Sometimes it emerges through
the third space. The subcostal may arise independently behind the
dorsal or from the superior cervical artery.
2. The =superior= or =deep cervical artery= (A. cervicalis profunda)
arises in front of the dorsal or by a common trunk with it. It crosses
the œsophagus (left side), the trachea (right side), and the longus
colli, and emerges from the thoracic cavity by passing through the space
behind the first costo-transverse articulation. In the thorax it gives
off a small branch (A. mediastini cranialis) to the mediastinum and the
pericardium; also the first intercostal artery (A. intercostalis prima),
a very small vessel which passes down in the first intercostal space.
After leaving the thorax the artery passes upward and forward on the
spinalis muscle and the lamellar part of the ligamentum nuchæ, covered
by the complexus. Its terminal branches anastomose with branches of the
occipital and vertebral arteries in the region of the axis. Numerous
collateral branches are detached to the extensor muscles of the head and
neck, the ligamentum nuchæ, and the skin, and anastomoses occur with the
dorsal artery above and the vertebral artery below.
The artery sometimes emerges through the second intercostal space.
[Illustration:
FIG. 430.—VERTEBRAL ARTERY OF HORSE. (After Schmaltz, Atlas d. Anat.
d. Pferdes.)
]
3. The =vertebral artery= (A. vertebralis) arises from the brachial (or
brachiocephalic) opposite the first intercostal space and passes upward
and forward. On the left side it crosses the œsophagus, on the right the
trachea. Emerging from the thorax it passes between the longus colli
internally and the scalenus externally, under the transverse process of
the seventh cervical vertebra, and continues along the neck through the
series of foramina transversaria, between which it is covered by the
intertransversales colli. Emerging from the foramen of the axis, it
crosses the capsule of the atlanto-axial joint, and joins the retrograde
branch of the occipital artery under cover of the great oblique muscle
of the head. At each intervertebral foramen a =spinal branch= (Ramus
spinalis) is given off which enters the vertebral canal and reinforces
the ventral spinal artery. It also gives off series of dorsal and
ventral =muscular branches= (Rami musculares). The dorsal branches are
the larger; they supply the deep extensor muscles of the head and neck,
and anastomose with the deep cervical and occipital arteries. The
ventral branches supply chiefly the scalenus, longus colli,
intertransversales, and rectus capitis anterior major. The artery is
accompanied by the vertebral vein and a sympathetic nerve-trunk.
In some cases the last cervical transverse process has a foramen
transversarium, through which the artery passes.
4. The =internal thoracic artery= (A. thoracica s. mammaria interna) is
a large vessel which arises from the ventral side of the brachial
opposite the first rib. It curves downward and backward, being at first
on the inner surface of the rib, and then crosses the lower part of the
first intercostal space and passes under the transversus thoracis
muscle. It runs backward under cover of that muscle over the
chondro-sternal joints to the eighth costal cartilage, where it divides
into asternal and anterior abdominal branches. At each intercostal space
two collateral branches are detached. The =intercostal branches= (Rami
intercostales) pass upward in the intercostal spaces and anastomose with
homonymous descending arteries. The lower branches detach small twigs to
the transversus thoracis, pleura, and pericardium, and pass out between
the costal cartilages as =perforating branches= (Rami perforantes) to
supply the pectoral muscles and skin, anastomosing with the external
thoracic artery. A very small pericardiaco-phrenic artery ascends in the
mediastinum on the left side, in the caval fold of pleura on the right
side; it supplies fine twigs to the pericardium and pleura and
accompanies the phrenic nerve to the diaphragm. In the young subject it
gives small branches (Aa. thymicæ) to the thymus gland. The =asternal
artery= (A. musculophrenica) passes along the ninth costal cartilage and
continues along the costal attachment of the transversus abdominis (Fig.
185). It gives off intercostal branches which anastomose with those
descending from the thoracic aorta, and twigs to the diaphragm and
transversus abdominis. The =anterior abdominal artery= (A. epigastrica
cranialis) is the direct continuation of the internal thoracic. It
passes between the ninth costal cartilage and the xiphoid cartilage,
runs backward on the abdominal surface of the rectus abdominis and then
becomes embedded in it (Fig. 466). It supplies the ventral wall of the
abdomen and anastomoses with the posterior abdominal artery.
5. The =external thoracic artery= (A. thoracica externa) is given off
from the ventral aspect of the brachial, usually at the inner surface or
anterior border of the first rib. It turns around the first rib below or
behind the brachial vein (when given off within the thorax) and passes
backward under the deep pectoral muscle; it is continued as a small
vessel in the panniculus carnosus, where it accompanies the external
thoracic (“spur”) vein. It sends branches to the pectoral muscles and
the axillary lymph glands.
This artery varies in origin and size. Not rarely it arises from the
internal thoracic or from the brachial outside of the thorax. In other
cases it arises by a common trunk with the inferior cervical. It may
be very small or even absent, in which case the perforating branches
of the internal thoracic compensate.
6. The =inferior cervical artery= (Truncus omo-cervicalis) arises
usually from the dorsal surface of the brachial opposite the first rib
or where that vessel winds around the rib. It is directed downward and a
little forward across the external surface of the jugular vein and the
deep face of the scalenus among the lymph glands at the thoracic inlet,
and divides into ascending and descending branches. The =ascending
branch= (A. cervicalis ascendens) passes upward and forward along the
external surface of the jugular vein, then turns sharply backward and
runs upward along the anterior border of the anterior deep pectoral
muscle, between the omo-hyoideus and mastoido-humeralis and in relation
to the prescapular lymph glands; it gives branches to these muscles and
the prepectoral and prescapular lymph glands. The =descending branch=
(A. transversa scapulæ) passes downward and outward across the surface
of the anterior deep pectoral and then runs in the groove between that
muscle and the mastoido-humeralis in company with the cephalic vein. It
supplies branches to these muscles and the skin of the breast.