220 HISTORY OF THE HUMAN BODY 



much remains to be accomplished. There has, indeed, been a 

 large amount of anatomical work done on the subject, but little 

 has as yet been attained in the study of the phylogenetic devel- 

 opment of the separate muscles or muscle groups, and the 

 morphological history of the limb muscles is as yet far from 

 complete. 



The key to the interpretation of the muscles associated with 

 the hand type of limb (chiropterygium) must be found, if at 

 all, among the tailed amphibians,. which are the first animals 

 to possess a true chiropterygium, that is, a free appendage 

 furnished with digits instead of fin-rays, and here, in fact, are 

 found many highly suggestive conditions, showing many of 

 the most characteristic muscles of the higher type still in partial 

 connection with the myotomes from which they have arisen. 

 On the other hand, a direct comparison of these muscles with 

 those of man and other mammals is by no means impossible 

 and yields many interesting results, since the distance between 

 these two groups of animals is much less than is commonly 

 supposed, and the intermediate stages do not include either the 

 tailless amphibians, the birds, or even the majority of reptiles, 

 since all these have specialized along lateral lines. Indeed, 

 man himself is far more primitive in the condition of his limbs, 

 with their ancient inheritance of pentadactylism, than are 

 either the salient Anura, with their four anterior digits and 

 their specialized hip-girdle, or such reptiles as the turtles, in 

 which both girdles have become much modified in connection 

 with the formation of carapace and plastron. 



Probably the most primitive living vertebrate, above the 

 fishes, is a large aquatic salamander, Necturus, generally dis- 

 tributed throughout the United States, except the Northeastern 

 States, and the extreme South. It may thus be assumed to 

 represent in the muscles of its free limbs the earliest condition 

 of chiropterygial musculature yet remaining to us, and is con- 

 sequently of the utmost importance in the present inquiry. It 

 will be remembered that in most vertebrates there exists a 

 certain close correspondence in the skeletal parts of anterior 

 and posterior limbs, a so-called serial homology, and in many 



