68 ANATOMY OF THE WOOD EAT 



M. extensor carpi radialis brevis (figs. 13, 15, 28) 

 has origin from the lateral epicondyloid ridge of the hu- 

 merus between the origins of the extensores digitorum com- 

 munis and carpi radialis longus. The latter muscle covers 

 most of it. It develops a broad tendon which is inserted 

 upon the medial dorsum of metacarpus three. 



M. supinator (fig. 28) is the deepest muscle of the 

 lateral antibrachium. It has origin by a stout tendon 

 from the lateral side of the annular ligament of the radius. 

 Insertion is upon the proximal half of the cranio-lateral 

 part of the radius. 



All of these extensor muscles of the forearm are innervated 

 by the deep branch of the radial, or interosseus nerve. 



D. MUSCLES OF THE HAND 



There are undoubtedly vestiges of a number of muscles 

 in the manus of this genus, but only four of them are suffi- 

 ciently distinct for certain differentiation without special 

 microscopical investigation. These are 



Mm. lumbricales abductor digiti quinti 



abductor pollicis brevis flexor poUicis 



Mm. lumbricales (fig. 15) apparently number four, and 

 there are, of course, several interossei present, but they are 

 so small and fragile that their definition is at best unsatis- 

 factory, and they, together with rudiments of such muscles 

 as the opponens, are not described. 



M. abductor pollicis brevis (fig. 15) is a mere shred 

 of muscle passing apparently from the base of the falciform 

 to the thumb. 



M. abductor digiti quinti (fig. 18) is a quite con- 

 spicuous muscle upon the lateral side of the palm. Origin 

 is from the pisiform, with insertion upon the proximal 

 phalanx of digit five. 



M. flexor pollicis (fig. 15) arises from the scapholunar 



