184 CIRCULATORY SYSTEM. 



place where the artery divides, it is covered by the humeral 

 plexus of veins, and by the absorbent glands of the arm. 



The ulnar artery consists of a common root from which 

 spring three or four vessels of considerable size running in waving 

 lines upon the inner surface of the lower end of the humerus. 

 The upper one, commonly the largest, is directed to the ulna ; 

 splitting, however, before it reaches the bone, and sending one 

 branch upward upon the olecranon, and another downward to the 

 heads of the flexors, to which muscles the other branches of this 

 vessel are exclusively distributed. 



The spiral artery, the outermost division, turns round 

 the OS humeri, and passes under the flexor brachii, sending a re- 

 current branch to it, to arrive at the front of the head of the 

 radius, where it splits into several branches, of which — I. Some 

 run into the elbow-joint. 2. Others, larger and more in num- 

 ber, penetrate the heads of the extensors. 3. Two long slender 

 ones descend upon the radius, under the extensor muscles, to 

 which they give branches in their course, as low as the front of 

 the knee, and there end in ramifications about and into the joint, 

 anastomosing with others coming from the radial. 



The radial artery, the principal division of the humeral, 

 continues its descent along the radius, inclining as it descends 

 from the inner to the back part of that bone; so that if it were 

 purposed to cut down upon it about the middle of the arm, the 

 incision should correspond in a line with the inner edge of the 

 radius, from which, to expose the vessel, the faschia must be 

 first detached, and afterwards the flexor metacarpi internus. The 

 radial nerve, which in this place accompanies it, runs upon its 

 outer side, but subsequently gets behind it. A short way above 

 the knee, it splits into the metacarpal arteries. It gives off — 



1. Small vessels to the elbow-joint. 2. Various branches to the 

 flexor muscles during its course. 3. The medullary artery of the 

 radius, at about one-fourth of the length of the bone downward. 



The small metacarpal artery descends, within a cel- 

 lular sheath, along the inner and back part of the knee, more 

 outwardly situated than the large one, from which it is separated 

 by the posterior annular ligament. It continues its descent along 

 with the metacarpal vein (which runs to its inner side) until it 

 arrives below the knee, where it bifurcates and transmits its divi- 

 sions down upon the front of the suspensory ligament — between 

 it and the cannon-bone. It sends off"—]. Cutaneous branches 

 over the front of the knee, which anastomose with the spiral. 



2. Ramifications to the front of the cannon. 3. To the suspen- 

 sory ligament. 



The large metacarpal artery, which may be regarded 



