660 BLOOD-VASCULAR SYSTEII OF THE HORSE 



branches to the skin, the tendon, the cofSn joint, and the coronary corium of the 

 hoof. 



4. The volar artery of the second phalanx (Ramus volaris phalangis secundse) 

 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 tertian) 

 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 circvunflex artery of the coronary cushion, an anastomotic 

 arch which lies on the extensor tendon at the coronet. In some oases 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 tertiae)' 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 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 oesophageal, which arise by a 

 broncho-oesophageal trunk. The parietal branches (Rami parietales) are the 

 intercostal and phrenic arteries. 



1. The broncho-oesophageal artery (Truncus broncho-oesophageus) is a short, 

 usually bulbous, trunk which arises at the sixth thoracic vertebra from the aorta or in 

 common ^^'ith 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 oesophageal branches. The bronchial artery (A. 

 bronchialis) crosses the left face of the oesophagus 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 oesophageal artery (A. oesophagea) (Fig. 554) is a small 

 vessel which passes backward dorsal to the oesophagus in the posterior mediastinum 

 and anastomoses with the oesophageal branch of the gastric artery. It detaches 

 twigs to the oesophagus 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. 



- In some cases there is no broncho-cesophageal trunk, the bronchial and oesophageal arising 

 separately. In other cases the second aortic intercostal arises in common with them also. 



