660 BLOOD-VASCULAR SYSTEM OF THE HORSE 
branches to the skin, the tendon, the coffin joint, and the coronary corium of the 
hoof. 
4. The volar artery of the second phalanx (Ramus volaris phalangis secunds) 
is smaller than the preceding, opposite to which it arises. It passes above the 
proximal border of the distal sesamoid and unites with the opposite artery. 
The arteries of the second phalanx form what is termed by Chauveau the coronary circle. 
The dorsal (anterior) part of the circle gives off commonly an artery (A. coronalis phalangis tertix) 
near either side of the extensor tendon, which divides into two branches. The central branch 
unites with that of the opposite side, while the other joins a branch of the artery of the digital 
cushion. In this way is formed the circumflex artery of the coronary cushion, an anastomotic 
arch which lies on the extensor tendon at the coronet. In some cases descending branches of the 
arteries of the first phalanx concur in the formation of the arch. 
5. The dorsal artery of the third phalanx (A. dorsalis phalangis tertia)! arises 
at the deep face of the angle of the third phalanx, passes through the notch or fora- 
men there, and runs forward in the groove on the dorsal surface. It gives off 
ascending and descending branches, which ramify in the corium of the wall of the 
hoof, anastomosing above with the circumflex artery of the coronary cushion and 
distally with the circumflex artery of the third phalanx. Before passing through 
the wing it detaches a retrograde branch to the digital cushion, and after emerging, 
one which ramifies on the convex surface of the cartilage of the third phalanx. 
BRANCHES OF THE THORACIC AORTA 
In addition to the coronary arteries and the common brachiocephalic trunk 
(which have been deseribed), 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 cesophageal, which arise by a 
broncho-cesophageal trunk. The parietal branches (Rami parietales) are the 
intercostal and phrenic arteries. 
1. The broncho-cesophageal artery (Truncus broncho-cesophageus) 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 descends (under cover of the 
vena azygos) over the right face of the aorta toward the bifurcation of the trachea 
and divides into bronchial and cesophageal branches. The bronchial artery (A. 
bronchialis) crosses the left face of the cesophagus to the bifurcation of the trachea, 
where it divides into right and left branches. Each enters the hilus of the cor- 
responding 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. The cesophageal artery (A. cesophagea) (Fig. 554) is a small 
vessel which passes backward dorsal to the cesophagus in the posterior mediastinum 
and anastomoses with the cesophageal branch of the gastric artery. It detaches 
twigs to the cesophagus and the mediastinal lymph glands and pleura, and 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 back- 
ward ventral to the oesophagus.” 
2. The intercostal arteries (Aa. intercostales) (Figs. 553, 554) 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 intercostal arteries arise from the dorsal face of the aorta in pairs close to- 
gether; 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 
vertebrae and the pleura, and divides into dorsal and ventral branches. The dorsal 
1 Also termed the preplantar artery. 
2 In some cases there is no broncho-cesophageal trunk, the bronchial and cesophageal arising 
separately. In other cases the second aortic intercostal arises in common with them also. 
