FOREARM AND HAND 139 



Pull the pronator teres laterally and secure the median nerve 

 as it emerges between the superficial and deep heads of the 

 muscle and before it disappears between the radial and humeral 

 parts of the flexor digitorum sublimis. Then clean the flexor 

 sublimis, being careful not to injure the thin sheet of fibres by 

 which it takes origin from the volar border of the radius. Clean 

 the four tendons in which the flexor sublimis terminates. They 

 are arranged in pairs, two anterior which pass to the middle and 

 ring fingers, and two posterior for the index and little fingers. 

 Pull upon the tendons and note the results. Note also that the 

 median nerve, after it emerges from between the two heads of 

 the pronator teres, disappears again between the humeral and radial 

 origins of the flexor sublimis to reappear at the lateral border 

 of the muscle a short distance proximal to the wrist, where it 

 lies under cover of the radial border of the tendon of the palmaris 

 longus. The tendons of the flexor digitorum sublimis must 

 not be followed further than the transverse carpal ligament at 

 present. The terminal parts will be displayed in a later dissection. 



Common Origin of the Superficial Muscles. The five 

 muscles which constitute the superficial group are very closely 

 associated with each other at the elbow indeed, they may 

 be said to arise by a common origin from the front of the 

 medial epicondyle of the humerus. In addition they all 

 derive fibres from the investing deep fascia of the limb, near 

 the elbow, and from the strong fibrous septa which pass be- 

 tween the muscles from the deep surface of investing fascia. 

 The pronator teres, the flexor sublimis, and the flexor carpi 

 ulnaris, have additional heads of origin (Figs. 61, 62). 



M. Pronator Teres. The pronator teres muscle crosses 

 the proximal half of the front of the forearm obliquely. It 

 arises by two heads, viz., a humeral and an ulnar. The 

 humeral head constitutes the chief bulk of the muscle. It 

 springs from the proximal part of the medial epicondyle of 

 the humerus, and also slightly, by fleshy fibres, from the distal 

 part of the medial epicondylar ridge. The fascia covering it 

 and the fibrous septum on its medial side also contribute fibres. 

 The ulnar head is placed deeply, and it may be recognised 

 from the fact that it intervenes between the median nerve 

 and the ulnar artery. The ulnar head is very variable in 

 size. As a rule, it is a small fleshy slip, but sometimes it is 

 chiefly fibrous. It arises from the medial border of the 

 coronoid process of the ulna (Fig. 64, p. 147), and soon 

 joins the deep surface of the humeral head. The muscle, 

 thus formed, passes obliquely distally and laterally, and ends 

 in a tendon which gains insertion into a rough impression 

 upon the middle of the lateral surface of the radius (Fig. 64, 



