DISSECTION OF THE ANTERIOR LIMB. 23 



the joint it again changes its position by mounting on the surface of 

 the artery, or it may even again place itself in front. At a variable 

 point in the fore-arm it terminates by dividing into two branches, one 

 of which is continued as the internal plantar nerve, while the other 

 joins the ulnar to form the external plantar. In the subject from 

 which Plate 6 was taken the division took place considerably above 

 the middle of the fore-arm, but more frequently it occurs in the lower 

 third. Immediately below the elbow the nerve furnishes a branch to 

 the internal flexor of the metacarpus, and branches to the deep flexor 

 of the digit (humeral and radial heads). 



Directions. — The muscles on the back of the fore-arm must now be 

 learnt. These consist of the three flexors of the metacarpus and the 

 two flexors of the digit. 



The Flexor Metacarpi Internus (Plate 6). This muscle lies along 

 the inner edge of the posterior surface of the radius, where it conceals 

 the posterior radial vessels and the median nerve. It arises from the 

 inner condyle of the humerus, just behind the point of origin of the 

 internal lateral ligament, where it is confounded with the origin of 

 the middle flexor. It terminates inferiorly in a long, slender tendon, 

 which, after passing through a synovial sheath at the inner side of the 

 carpus, is inserted into the head of the inner small metacarpal bone. 



Action. — It is a flexor at the carpal articulations — i.e., it flexes the 

 maims on the fore-arm. 



The Flexor Metacarpi Medius (Plate 6). This muscle descends in 

 contact with the posterior edge of the internal flexor. It has two heads 

 of origin — an anterior and a posterior. It arises by its anterior head 

 just behind the origin of the preceding muscle, and by its posterior 

 head from the upper part of the posterior edge of the olecranon. After 

 a course of three or four inches these two heads unite, and the single 

 inferior tendon is inserted into the upper border of the pisiform bone. 

 The ulnar nerve and vessels pass beneath the posterior or ulnar head 

 of the muscle. 



Action. — The same as the preceding muscle. 



The Flexor Metacarpi Externus (Plates 7 and 8) is situated at the 

 outer side of the back of the fore-arm, having the lateral extensor of the 

 digit (extensor suffraginis) in front of it, while behind it is separated 

 from the last-described muscle by the ulnar division of the deep-flexor 

 of the digit (ulnaris accessorius). It arises from the lowest point of the 

 outer condyle of the humerus. At its lower end it has two insertions, 

 viz., (1) into the upper border of the pisiform bone, where it is con- 

 founded with the insertion of the middle flexor ; (2) by a cord-like 

 tendon which, after descending in a synovial sheath formed inwardly 

 by the oblique groove on the outer surface of the pisiform bone, is 

 inserted into the head of the external small metacarpal bone. 



