230 HISTORY OF THE HUMAN BODY 



which extends in urodeles from the sides of the tail to the 

 ischium and femur, persists with some modifications in mam- 

 mals ; in man and the higher anthropoids, in which the reduc- 

 tion of the caudal vertebras restricts the origin, the group is 

 represented by a single muscle, the piriformis, extending from 

 the coccygeal region across to the femur. 



The muscles of the distal portion of the vertebrate chirop- 

 terygium, that is, from elbow or knee on, aside from the mod- 

 ifications imposed upon them by the varying shapes of the 

 limbs themselves, and the great difference in their use, are, in 

 their essential features, quite similar in all living forms, and 

 in their differences show the modifications of a primary type 

 due to environment rather than the suggestions of an historic 

 development of that type. The study is, therefore, one mainly 

 of the adaptations of a given set of elements, rather than a 

 phylogenetic history, which latter, as is the case also with the 

 bones of the same region, must be sought in the gap separating 

 fin and hand, that is, in the phylogenetic stages represented 

 by lost forms of ganoids, stegocephali, and their allies. The 

 salamander Necturus, probably the nearest approach to this 

 series represented by living fauna, offers in its distal muscles 

 some few suggestions of an earlier phylogenetic stage, and is 

 thus of fundamental importance in the present inquiry. The 

 well-nigh complete correspondence in the fore and hind limb 

 as regards not only bones and muscles, but other parts as well, 

 has been commented on above and offers strong support for 

 the doctrine of serial homology, to be considered later. There 

 are, also, as is the case with higher forms, some traces of a 

 correspondence between the dorsal and ventral surfaces of a 

 single paw, giving a suggestion of the derivation of the 

 chiridial musculature from a fin-like precursor, in which the 

 jointed rays (digits) were supplied by similar muscular ele- 

 ments applied both dorsally and ventrally, as in present-day 

 fishes. The following description is that of the anterior limb, 

 but with the substitution of the terms tibia and fibula for radius 

 and ulna, tarsus for carpus, and so on, it will be found almost 

 equally applicable to the posterior one. In a few cases a muscle 



