454 MYOLOGY 



passing from the same tendon downward and medialward to the fourth. Occa- 

 sionally the first tendon is connected to the second by a thin transverse band. 



Variations. An increase or decrease in the number of tendons is common; an additional slip* 

 to the thumb is sometimes present. 



The Extensor digit! quinti proprius (Extensor minimi digiti) is a slender muscle 

 placed on the medial side of the Extensor digitorum communis, with which it is 

 generally connected. It arises from the common Extensor tendon by a thin 

 tendinous slip, from the intermuscular septa between it and the adjacent muscles. 

 Its tendon runs through a compartment of the dorsal carpal ligament behind the 

 distal radio-ulnar joint, then divides into two as it crosses the hand, and finally 

 joins the expansion of the Extensor digitorum communis tendon on the dorsum 

 of the first phalanx of the little finger. 



Variations. An additional fibrous slip from the lateral epicondyle; the tendon of insertion may 

 not divide or may send a slip to the ring finger. Absence of muscle rare; fusion of the belly with 

 the Extensor digitorum communis not uncommon. 



The Extensor carpi ulnaris lies on the ulnar side of the forearm. It arises 

 from the lateral epicondyle of the humerus, by the common tendon; by an aponeu- 

 rosis from the dorsal border of the ulna in common with the Flexor carpi ulnaris 

 and the Flexor digitorum profundus; and from the deep fascia of the forearm. 

 It ends in a tendon, which runs in a groove between the head and the styloid 

 process of the ulna, passing through a separate compartment of the dorsal carpal 

 ligament, and is inserted into the prominent tubercle on the ulnar side of the base 

 of the fifth metacarpal bone. 



Variations. Doubling; reduction to tendinous band; insertion partially into fourth metacarpal. 

 In many cases (52 per cent.) a slip is continued from the insertion of the tendon anteriorly 

 over the Opponens digiti quinti, to the fascia covering that muscle, the metacarpal bone, the 

 capsule of the metacarpophalangeal articulation, or the first phalanx of the little finger. This slip 

 may be replaced by a muscular fasciculus arising from or near the pisiform. 



The Anconasus is a small triangular muscle which is placed on the back of the 

 elbow-joint, and appears to be a continuation of the Triceps brachii. It arises 

 by a separate tendon from the back part of the lateral epicondyle of the humerus; 

 its fibers diverge and are inserted into the side of the olecranon, and upper fourth 

 of the dorsal surface of the body of the ulna. 



The Deep Group (Fig. 419). 



Supinator. Extensor pollicis brevis. 



Abductor pollicis longus. Extensor pollicis longus. 



Extensor indicis proprius. 



The Supinator (Supinator brevis) (Fig. 420) is a broad muscle, curved around 

 the upper third of the radius. It consists of two planes of fibers, between which 

 the deep branch of the radial nerve lies. The two planes arise in common the 

 superficial one by tendinous and the deeper by muscular fibers from the lateral 

 epicondyle of the humerus; from the radial collateral ligament of the elbow-joint, 

 and the annular ligament; from the ridge on the ulna, w r hich runs obliquely down- 

 ward from the dorsal end of the radial notch ; from the triangular depression below 

 the notch; and from a tendinous expansion which covers the surface of the muscle. 

 The superficial fibers surround the upper part of the radius, and are inserted into 

 the lateral edge of the radial tuberosity and the oblique line of the radius, as low 

 down as the insertion of the Pronator teres. The upper fibers of the deeper plane 



