THE VASCULAR SYSTEM 213 



a second branch of the ulnar artery — R. recurrens ulnaris anterior — 

 which leaves the A. ulnaris at about the middle of the fore-arm. 



After giving off the ulnar artery the A. interossea passes to the 

 extensor side of the M. interosseus. Immediately after doing so it 

 gives off a branch which passes out at right angles, through the origin 

 of the M. extensor antibrachii ulnaris, to the skin of the ulnar side of 

 the elbow and fore-arm. It is the A. collateralis ulnaris^ and its twigs 

 fuse with those of the R. recurrens ulnaris and also with a terminal 

 twig of the A. profunda brachii which probably represents the R, 

 collateralis radialis. 



At about the same level the A. interossea gives off a large branch 

 which, after giving a small twig to the M. interosseus, turns dorsally 

 and comes to lie immediately underneath the M. extensor digitorum 

 communis. It is the second main branch of the interosseal artery. 



(ii) The A. interossea externa (Zuckerkandl), or A. perforans 

 superior (Osawa), spreads over the dorsum of the fore-arm and carpus, 

 and supplies the extensor muscles. Three of its branches are worthy 

 of note. First, the R, recurrens posterior passes backwards along 

 the fore-arm and fuses with a branch — R. collateralis posterior — 

 from the A. profunda brachii. The second passes over the carpus 

 and supplies the M. abductor et extensor digiti I, and may finally 

 unite with the A. perforans carpi. The third passes out to the skin 

 on the ulnar side of the wrist and sends a branch to the ulnar 

 side of the fourth digit, where it joins the arcus dorsalis from the A. 

 perforans carpi. 



The A. interossea proper passes along the fore-arm, just dorsal to 

 the M. interosseus, without further branching. At the level of the 

 ulnare + intermedium it divides, and the larger branch penetrates 

 a foramen in this bone as the A. -perforans carpi (q.v.), while the 

 smaller continues the direction of the main vessel for a short distance 

 and then spreads over the palm of the hand supplying the short flexor 

 muscles of the digits — A. volaris. 



The A. perforans carpi^ after reaching the dorsal side of the hand, 

 runs forwards to the level of the bases of the metacarpals, and then 

 divides into two branches. Of these the pre-axial divides again so as 

 to supply the adjoining sides of digits i and 2, and 2 and 3 — the 

 pre-axial side of the first digit being supplied by the radial artery. 

 The post-axial branch of the A. perforans carpi divides to supply 

 the adjoining sides of digits 3 and 4, and gives off a twig which 

 crosses the base of the fourth digit to anastomose with a branch of 

 the A. interossea externa and supply the post-axial side of that 

 finger. 



