398 THE MUSCULAK SYSTEM. 



can take place separately. In extension of the inter-phalangeal joints, the muscle is aided by 

 the interossei and lumbrical muscles. 







M. Extensor Digit! Quinti Proprius. The extensor digiti quinti proprius 

 has an origin, similar to and closely connected with that of the preceding muscle, 

 from the common tendon, the fascia over it, and from interrnuscular septa. 



It passes along the dorsum of the forearm, as a narrow fleshy slip, between the 

 extensor digitoruin communis and the extensor carpi ulnaris, and ends in a tendon, 

 which occupies a groove between the radius and ulna in a special compartment 

 of the dorsal carpal ligament. On the dorsum of the hand the tendon, usually 

 split into two parts, lies on the medial side of the tendons of the extensor 

 digitorum communis, and is finally inserted into the expansion of the extensor 

 tendon on the dorsum of the first phalanx of the little finger. 



Nerve-Supply. The dorsal interosseous nerve (C. (5.) 6. 7. 8.). 

 Actions. The muscle extends the elbow, wrist, and little finger. 



M. Extensor Carpi Ulnaris. The extensor carpi ulnaris has a double origin : 

 (1) from the common tendon from the lateral epicondyle of the humerus, from the 

 fascia over it, and from the inter muscular septa ; and (2), through the medium of 

 the deep fascia, from the dorsal margin of the ulna in its middle two-fourths. 



Lying in the forearm upon the dorsal surface of the ulna, it ends in a tendon 

 which occupies a groove on the dorsal surface of the ulna in a special compartment 

 of the dorsal carpal ligament, and is inserted into the medial side of the base of 

 the fifth metacarpal bone (Fig. 353, p. 394). 



Nerve-Supply. The dorsal interosseous nerve (C. (5.) 6. 7. 8.). 



Actions. The muscle is an extensor of the wrist, and at the same time, acting with the 

 flexor carpi ulnaris it is a powerful adductor of the wrist. Its humeral attachment makes it also 

 a subordinate extensor of the elbow-joint. 



M. Anconseus. The anconaeus is a small triangular muscle. It arises, by a 

 separate tendon, from the distal part of the dorsal surface of the lateral epicondyle 

 of the humerus (Fig. 341, p. 380), and from the dorsal part of the capsule of 

 the elbow-joint. 



It covers part of the dorsal surface of the elbow- joint and proximal part of 

 the ulna, and is inserted, by fleshy fibres, into a triangular surface on the lateral 

 aspect of the olecranon and dorsaLsurface of the ulna, as far distally as the oblique 

 line (Fig. 355, p. 397). It is also inserted into the fascia which covers it. 



The epitrochleoanconseus is an occasional small muscle which arises from the dorsal surface 

 of the medial epicondyle of the humerus, and is inserted into the medial side of the olecranon. 

 It covers the ulnar nerve in its passage to the forearm. 



Nerve-Supply. The muscle is supplied by the terminal branch of the nerve to the medial 

 head of the triceps muscle from the radial (C. 7. 8.). 



Actions. The anconaeus is an extensor of the elbow. 



Deep Muscles. 



M. Supinator. The supinator muscle (O.T. supinator radii brevis) is the 



most proximal of the deeper muscles. It is almost wholly concealed by the 

 superficial muscles, and has a complex origin, (1) from the lateral epicondyle 

 of the humerus ; (2) from the radial collateral, and annular ligaments of the 

 elbow-joint ; (3) from the triangular surface on the shaft of the ulna just distal 

 to the radial notch ; and (4) from the fascia over it. 



From this origin the muscle spreads laterally and distally, enveloping the 

 proximal part of the radius, and is inserted into the volar and lateral surfaces of 

 the bone, as far forwards as the tubercle of the radius, as far proximally as the 

 neck, and as far distally as the oblique line and the insertion of the pronator teres 

 (Figs. 348, p. 389, and 355, p. 397). 



The muscle is divisible into superficial and deep parts with humeral and ulnar 

 origins, between which the deep branch of the radial nerve passes in its course 

 to the dorsal part of the forearm. 



