THE ARMY HORSE. 37 



brachial. The coiiiinoii carotid is short and iimiiediately 

 divides into tAvo branches, right and left carotids, wliich pass 

 up the neck, at first under the trachea and tlien on either side ; 

 they follow the trachea to the throat, where they divide into 

 branches, supplying the head. 



The brachial arteries continue toward the front part of the 

 thorax, winding- around the first ribs, and divide into branches, 

 supplying the fore limbs. The main branch of each is here 

 named the humeral artery. 



The humeral artery descends along the inner side of the 

 humerus and just above the elbow joint, divides into the 

 anterior and posterior radial arteries. 



The anterior radial descends over the front surface of the 

 elbow joint, passes down in front of the radius, and approaches 

 the knee below the extensor pedis muscle, where it divides into 

 numerous branches, suppljdng blood to the surrounding tissues. 

 The posterior radial is a continuation of the humeral arter}", 

 passing down the inner side of the fore leg, inclining back and 

 dividing at the lower end of the radius into the large and small 

 metacarjml arfejies. 



The small metacarjyal passes outward from the inner and 

 back part of the knee and, running downward, supplies nour- 

 ishment to the surrounding tissues. The large metacarpal is a 

 continuation of the posterior radial. It runs down the back of 

 the knee, in companj^ with the flexor tendon; above the fetlock 

 it passes between the tendon and the suspensory ligament, 

 dividing into the external and internal digital arteries, which 

 suppl}' 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 back- 

 ward, and reaches the left side of the spine just below the sixth 

 or seventh dorsal vertebra. 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 



