40 TOPOGEAPHICAL ANATOMY OF 



ulna. Thereupon it runs in a distal direction following the extensor 

 digiti quinti closely, and ends near the carpus in the rete carpi dorsale. 

 It furnishes branches to the adjacent muscles, and gives origin to two 

 named arteries. (1) A. nutritia radii (the nutrient artery of the 

 radius) arises as the interosseous artery passes between the two bones 

 of the forearm and immediately disappears into the radius. (2) A. 

 interossea recurrens (recurrent interosseous artery) is very small and 

 sometimes difficult to demonstrate. It has its origin close to the gap 

 between the radius and the ulna, runs upwards on the lateral surface of 

 the ulna, and anastomoses with branches of the deep artery of the arm 

 and the collateral ulnar artery. 



Eete carpi doesale. — The dorsal rete 1 of the carpus consists of a 

 network of small arteries lying over the distal end of the radius and 

 the dorsal surface of the carpus. It is formed by branches from the 

 collateral radial and dorsal interosseous arteries, and from it arise 

 the two dorsal metacarpal arteries (a. metacarpea dorsalis medialis: 

 a. metacarpea dorsalis lateralis) that follow the grooves between the 

 metacarpal bones and anastomose with the volar metacarpal arteries. 



Before leaving this region the dissector should take the opportunity 

 to examine the insertion of the biceps and brachials muscles. The 

 strong tendon of the biceps is attached to the tuberosity of the radius, 

 but a slender continuation can be followed under the medial collateral 

 ligament as far as the edge of the ulna. 



The brachial muscle is inserted mainly to the border of the radius 

 at a point just distal to the tuberosity. Some tendinous fibres pass 

 underneath the medial collateral ligament and blend with the trans- 

 verse ligament that joins the ulna to the radius. 



Dissection. — The dissector must now turn his attention to the struc- 

 tures lying behind the radius, and, of these, the muscles should be 

 examined first. So far as position is concerned, the extensor carpi 

 ulnaris could legitimately be included in the group of muscles which now 

 fall to be examined ; but, for morphological reasons, and because it is 

 supplied by the radial nerve, this muscle has already been dissected. 



The muscles lying behind the radius may be considered as disposed 

 in three strata: (1) The most superficial, enumerated from the radial 

 to the ulnar border of the limb, are : Mm. flexor carpi radialis, flexor 

 carpi ulnaris, flexor digitorum profundus (caput ulnare), extensor carpi 

 ulnaris. (2) The second layer consists of mm. flexor digitorum sub- 

 limis, flexor digitorum profundus (caput humerale). (3) The third 

 layer is of limited extent and formed solely by the radial head of the 

 deep flexor of the digits. 



1 Rete [L.], a net. 



