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 (£).—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 carpiulnaris. 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 third 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 (c) 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 interossee (¢) 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. Each 
of these interosseous arteries sends off muscular branches (e) to 
the short muscles in the palm, and branches into the fibrous 
pad which occupies the palm of the hand. The palmar arch 
