300 THE CIRCULATORY SYSTEM. 



substance of the pronator quadratus, which it supplies. It 

 sends a branch to the dorsal surface of the wrist; this ramifies 

 on the carpus, forming- a network of small arteries. 



5. A. ulnaris {k). — The ulnar artery passes beneath the 

 second, third, and fourth parts of the flexor profundus digitorum 

 (but outside of the origin of the fifth part), to the inner surface 

 of the flexor carpi ulnaris. It supplies the flexor carpi ulnaris, 

 the flexor profundus and palmaris longus, and passes on the 

 inner surface of the flexor carpi ulnaris to the wrist. Near the 

 wrist it sends a branch onto the side of the forearm, and 

 another to its midventral part, and ends in a small branch 

 to the wrist on the radial side of the pisiform bone. This 

 branch anastomoses with the radial to form the palmar arch, 

 described below. 



6. The palmar arch (Fig. 124) is formed by the termina- 

 tion of the radial artery [a) in the palm and its junction with 

 the end of the ulnar (/). The radial artery reaches the palm 

 between the bases of the second and third metacarpals and 

 passes thence toward the ulnar side and distad, piercing the 

 interosseus muscle of the third digit and lying on the outer 

 surface of the interossei of the thin! and fourth digits beneath 

 the adductors of the second and fifth digits. A small com- 

 municating branch from the radial passes to it between the first 

 and second metacarpals. 



Branches of the palmar arch : 



A. princeps pollicis et indicis (r) leaves the palmar arch 

 near its radial end and sends a branch onto the ulnar side of 

 the thumb and one onto the radial side of the index. 



The palmar interosseae {d) are three in number. They 

 leave the palmar arch (//) and pass distad and dorsad in the 

 intervals between the four ulnar digits. The radial one passes 

 along the ulnar side of the first digit, the ulnar one along the 

 radial side of the fifth digit. The middle one divides and sup- 

 plies the contiguous sides of the third and fourth digits. ICach 

 of these interosseous arteries sends off muscular branches (c) to 

 the short muscles in the palm, and branches into the fibrous 

 pad which occupies the palm of the hand. The palmar arch 



