The great arterial trunks in the thorax resemble those of the horse in
general disposition.
The =left coronary artery= is much larger than the right one; it gives
off a branch which descends in the intermediate groove, and terminates
by running downward in the right longitudinal groove. The =right
artery=, after emerging from the interval between the right auricle and
the pulmonary artery, divides into branches which are distributed to the
wall of the right ventricle.
The =brachiocephalic trunk= (anterior aorta) is usually four or five
inches (ca. 10 to 12 cm.) in length.
The =brachial arteries= give off in the thorax the following branches:
1. A common trunk for the subcostal, dorsal, superior or deep cervical,
and vertebral arteries.
(1) The =subcostal artery= commonly arises separately, but may be given
off as in the horse. It supplies the first three intercostal arteries.
(2) The =dorsal artery= is relatively small. It usually ascends in front
of the first costo-vertebral joint and is distributed as in the horse.
(3) The =superior= or =deep cervical artery= may arise from a common
stem (Truncus vertebro-cervicalis) with the vertebral, or may constitute
a branch of that artery. It passes up between the first thoracic and
last cervical vertebræ or between the sixth and seventh cervical and is
distributed as in the horse.
(4) The =vertebral artery= passes along the neck as in the horse to the
intervertebral foramen between the second and third cervical vertebræ,
gives off a muscular branch, and enters the vertebral canal (Fig. 469).
It runs forward on the floor of the canal—connected with its fellow by
two or three transverse anastomoses—and divides in the atlas into two
branches. The smaller internal division (cerebrospinal artery) passes
forward to the floor of the cranium and concurs with the condyloid
artery and branches of the internal maxillary in the formation of a
large =rete mirabile=. The large external branch emerges through the
intervertebral foramen of the atlas and ramifies in the muscles of the
neck in that region, compensating for the smallness of the branches of
the occipital artery. It also sends a branch to the rete mirabile. The
collateral branches detached to the cervical muscles are large and
compensate for the small size of the deep cervical artery. The
collateral spinal branches of the vertebrals pass through the
intervertebral foramina, divide into anterior and posterior branches,
and form two longitudinal trunks which are connected by cross-branches
so as to form irregular polygonal figures.