ANATOMY. 35 



tendon and the suspensory liji^ament, dividing into the external and 

 internal digital arteries, which supply the foot. 



The study of the digital arteries will be taken up later, when the 

 student has a more extended knowledge of the bones and of the 

 elastic and sensitive structures of the foot. 



We will now return to the posterior aorta. The posterior aorta is 

 larger and longer than the anterior. It begins at about the level of 

 the fourth dorsal vertebra, passes upward and backward, and reaches 

 the left side of the spine just below the sixth or seventh dorsal verte- 

 bra. It then passes straight back into the abdominal cavity and 

 terminates in the lumbar region below the last lumbar vertebra. 

 During its passage to this point it gives off branches to the muscles 

 of the ribs, to the lungs for their nourishment, to the abdominal 

 organs, and to the muscles of the loins. Below the last lumbar 

 vertebra it divides into four branches, the right and left external and 

 internal iliacs, which supply blood to the hind extremities. 



The internal iliacs are short thick trunks which soon break up into 

 several branches to the muscles of the hind quarters. The external 

 iliacs, with their continuations, are the main arteries of the hind legs. 

 Each, as previously stated, begins below the last lumbar vertebra, 

 curves obliquely outward and downward, giving off branches, and, 

 near the head of the femur, receives the name of femoral artery. 



The femoral artery is the artery of the thigh. Just above the back 

 of the stifle joint it divides into two branches, the anterior and pos- 

 terior tibial, the latter supplying the back part of the gaskin and hock 

 with nourishment, while the former winds forward between the tibia 

 and fibula to the fore part of the leg, gaining it midway between the 

 stifle and the hock. At the hock it passes obUquely outward, cross- 

 ing the joint, and becomes the great metatarsal artery at the upper and 

 outer part of the metatarsus. The great metatarsal passes under the 

 small splint bone and gains the back part of the cannon, then, passing 

 down the leg, it divides just below the fork of the suspensory Hgament 

 into two branches, the external and internal digitals, which will be 

 studied later. 



The involuntary muscles of the heart receive their blood supply 

 from two small arteries, right and left coronary, which branch off at 

 the beginning of the common aorta. 



Veins. 



Veins are usually found accompanying the arteries of the body and 

 bearing similar names; there are several important exceptions, 

 three of which will be here noted, namely, the anterior vena cava, 

 jugular, and posterior vena cava. 



The anterior vena cava is the large, short vein, formed by numerous 

 branches, returning the blood from the head, the neck, the fore leg. 



