52 THE ANATOMY OF VERTEBRATED ANIMALS. 



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

 such as the extensor proprius hidicis and extensor minimi 

 diglti^ are only remains of muscles which are more fully de- 

 veloped in lower mammals, and send tendons to all four of 

 the ulnar digits. 



Only the pollex has an opponens.^ Only the pollex and 

 hallux have adductors and abductors. Some of the dioits 

 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 their 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 extensors 

 of the digits of the pes arise from the femur, while some of 

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

 seem to be, as it were, higher up in the fore-limb than in the 

 hind-limb. Nevertheless, several of the muscles corresj)ond 

 very closely. Thus, on the dorsal aspect, the extensor ossis 

 m,etacar2n polUcis passes from the post-axial side of the proxi- 

 mal region of the antebrachium obliquely to the trapezium 

 and the metacarpal of the pollex, just as its homologue, the 

 tibialis anticus, passes from the post-axial side of the upper 

 part of the leg to the entocuneiform and the base of the me- 

 tatarsal of the hallux ; the two muscles correspond exactly. 

 But the extensors of the phalanges of the pollex, and the deep 

 extensors of the other digits of the manus, arise on the same 

 side of the antebrachium, below the extensor ossis metacarpi 

 pollicis y while, in the leg, one of the deep extensors of the 

 hallux, and all those of the other digits, arise still lower 

 down, viz., from the calcaneum. 



Not less remarkable is tlie contrast between the more 

 superficial sets of extensors in the two limbs. In the fore 

 limb, proceeding from the pre-axial to the post-axial side, the 

 following extensor muscles arise from the external or pre- 

 axial condyle of the humerus : the extensor carpi radicdis lon- 

 gus to the base of the second metacarpal ; the extensor carpi 

 radialis brevis to the base of the third metacarpal ; the exten- 

 sor communis digitorum to the four ulnar digits ; the exte?i' 

 sor minimi digiti to the fifth digit ; the extensor carpi ul 



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



