102 THE UPPER EXTREMITY 



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. To bring it into view the superficial 

 humeral head must be drawn well to the medial side. 

 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. 43, p. 1 08), and soon joins the deep surface of the 

 numeral head. The muscle thus formed is carried 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. 43, p. 108). This attach- 

 ment is placed on the summit of the chief curve of the 

 radius, an arrangement which enables the muscle to exercise 

 its pronating action at a great advantage. Close to its 

 insertion the pronator teres is crossed by the radial artery 

 and is covered by the brachioradialis muscle. It is supplied 

 by the median nerve. It is a pronator of the forearm and 

 hand and a flexor of the elbow. 



M. Flexor Carpi Eadialis. The flexor carpi radialis arises 

 from the common tendon, from the fascia of the forearm 

 and the fibrous septa which intervene between it and the 

 adjacent muscles. Its fleshy belly gives place, a short distance 

 distal to the middle of the forearm, to a long flattened tendon, 

 which, at the wrist, traverses the groove on the front of the 

 os multangulum majus in a special compartment of the trans- 

 verse carpal ligament (Fig. 48, p. 122). It is inserted into 

 the volar aspect of the base of the metacarpal bone of the 

 index, and slightly also into the base of the metacarpal bone 

 of the middle finger. Its relations to the transverse carpal 

 ligament, and also its attachment to the metacarpus, will be 

 exposed and studied at a later stage of the dissection. It 

 is supplied by the median nerve. 



M. Palmaris Longus. This is a long slender muscle, which 

 is not always present. It springs from the common origin, 

 the aponeurotic investment of the forearm and the fibrous 

 septum on either side of it. Its tendon pierces the deep fascia 

 immediately proximal to the wrist, and then proceeds distally, 

 in front of the transverse carpal ligament, to join the strong 

 intermediate portion of the palmar aponeurosis. Very 

 frequently it gives a slip to the abductor pollicis brevis. It is 



