In addition to the coronary arteries and the common brachiocephalic
trunk (which have been described), the thoracic part of the aorta gives
off branches to the thoracic walls and viscera and to the spinal cord
and its membranes. The =visceral branches= (Rami viscerales) are the
bronchial and œsophageal, which arise by a broncho-œsophageal trunk. The
=parietal branches= (Rami parietales) are the intercostal and phrenic
arteries.
1. The =broncho-œsophageal= (Truncus broncho-œsophageus) is a short,
usually bulbous, trunk which arises at the sixth thoracic vertebra from
the aorta or in common with the first aortic intercostal arteries. It
passes (under cover of the vena azygos) down the right face of the aorta
toward the bifurcation of the trachea and divides into bronchial and
œsophageal branches.
(_a_) The =bronchial artery= (A. bronchialis) crosses the left face of
the œsophagus to the bifurcation of the trachea, where it divides into
right and left branches. Each enters the hilus of the corresponding lung
above the bronchus, which it accompanies in its ramification. It
supplies the lung tissue and also detaches twigs to the bronchial lymph
glands and the mediastinum.
(_b_) The =œsophageal artery= (A. œsophagea) (Fig. 429) is a small
vessel which passes backward above the œsophagus in the posterior
mediastinum and anastomoses with the œsophageal branch of the gastric
artery. It detaches twigs to the œsophagus and the mediastinal lymph
glands and pleura, and also gives off two branches which pass between
the layers of the ligaments of the lungs and ramify in the subpleural
tissue. Very commonly there is another artery which runs backward
ventral to the œsophagus.
In some cases there is no broncho-œsophageal trunk, the bronchial and
œsophageal arising separately. In other cases the second aortic
intercostal arises in common with them also.
2. The =intercostal arteries= (Aa. intercostales) (Figs. 428, 429)
number eighteen pairs. The first arises from the deep cervical artery,
the next three from the subcostal branch of the dorsal artery, and the
remainder from the aorta. The aortic intercostals arise from the dorsal
face of the aorta in pairs close together; the fifth and sixth usually
spring from a common stem. Each passes across the body of a vertebra to
the corresponding intercostal space, detaches twigs to the vertebræ and
the pleura, and divides into dorsal and ventral branches. The =dorsal
branch= (Ramus dorsalis) gives off a spinal branch (Ramus spinalis)
which passes through the intervertebral foramen, gives twigs to the
membranes of the spinal cord, perforates the dura, and reinforces the
ventral spinal artery. A muscular branch passes to the muscles and skin
of the back. The =ventral branch= (Ramus ventralis) is much the larger.
It passes downward, at first almost in the middle of the intercostal
space between the intercostal muscles, then gains the posterior border
of the rib and is subpleural. Each is accompanied by a vein and nerve,
the artery being in the middle and the vein in front. At the lower part
of the space it unites with a ventral intercostal branch of the internal
thoracic or the asternal artery. It supplies the intercostal muscles,
the ribs and the pleura, and gives off perforating branches which pass
out to the serratus magnus, the abdominal muscles, and the skin.
3. The =phrenic arteries= (Aa. phrenicæ) are two or three small vessels
which arise at the hiatus aorticus from the ventral aspect of the aorta,
often by a common trunk. They supply the crura of the diaphragm. In some
cases they arise in common with an intercostal artery.