54 THE ANATOMY OF VEETEBRATED ANIMALS. 



to the base of the metatarsal ; secondly, two interossei ; 

 thirdly, a perforated flexor; and fourthly, a perforating 

 flexor, like those of the manus. The divisions of the inter- 

 ossei, which send tendons to the extensor sheath on the 

 dorsum of the digits of the foot in Man, are hardly distinct 

 from the ventral divisions of those muscles. 



In addition to the muscles which have been mentioned, 

 the fifth digit has an abductor and an adductor, which may 

 be regarded as subdivisions of the interossei, arising within 

 the manus or pes, and insei"ted into opposite sides of the 

 proximal phalanx ; and an opponens, a muscle attached to the 

 ventral face of the carpus or the tarsus, and inserted into the 

 post-axial edge of the shaft of the metacarj^al or metatarsal. 



Finally, a lumbricalis muscle proceeds from the tendon 

 of the perforating flexor, on the pre-axial side of the digit, 

 to the extensor sheath. 



None of the other digits of the manus, or of the pes, has a 

 greater number of muscles than this ; in fact, all the others 

 have fewer muscles, some of those enumerated being sup- 

 pressed. What are often regarded as muscles special to man, 

 siich as the extensor proprius indicis and extensor minimi 

 digiti, are only remains of muscles which are more fully 

 developed in lower mammals, and send tendons to all four 

 of the ulnar digits. 



Only the pollex has an opponens* Only the poUex and 

 hallux have adductm-s and abductors. Some of the digits 

 lack one or more of the ventral, or of the dorsal, muscles. 



The correspondence between the muscles which have been 

 mentioned, at their insertion in the digits, is clear enough, 

 but some difficulties present themselves when the muscles 

 are traced to theii- origins. 



In Man the flexors and extensors of the digits (except the 

 interossei) of the fore limb, arise in part from the humerus, 

 and in part from the bones of the forearm, but not within 

 the manus. On the contrary, none of the flexors and ex- 

 tensors of the digits of the pes arise from the femiu-, while 

 some of them arise within the pes itself. The origins of 

 * I have seen an opponens in the hallux of an Orang. 



