ANATOMY OF CACOPUS SYSTOMA. 



551 



viz. the joars-cZafic^t/rtris. It would also appear that as the 

 functions of these two muscles of the chest have become reduced 

 to a minimum in this toad, a large size and an extensive origin 

 for the same have been rendered vmnecessary. According to 

 Ecker (4), in Rana the sterno-radicdis is a powerful flexor of the 

 fore-arm, and the deltoideus draws the same limb forwards. These 

 movements, though essential to a good swimmer, are in all 

 probability of only a limited use to a teiu^estrial frog. Thus it 

 becomes difficult to say whether the vestigial condition of the 

 chest-muscles led to the disappearance of certain of the elements 

 of the pectoral girdle, or the latter condition necessitated the 



Text-figure 18. 



A ventral view of the trunk and a thigh with the skin cut open in order to show 

 the relation of certain muscles with the skin. I., several tibres of the rectus- 

 internns-minor (R.l'.) arising from the skin (SK.) on the lower surface of a thigh ; 

 A., the region of the skin from which the outer division of the portio-abdominis 

 starts and to which that of the rectus-abdominis is inserted ; S., sartorius ■ 

 R.I., rectiis-internus-major ; V.I., vastus-internus. 



former. It is more probable that the two degenerative processes 

 might have pi"oceeded concomitantly. 



On the contrary, one finds that the portio-sternalis-anterior 

 and the portio-abdominis muscles have attained a great develop- 

 ment, and the outer division of the latter has become partially 

 converted into a cutaneous muscle (text-fig. 18). The attach- 

 ment to the skin has, I should think, given additional purchase 

 to this muscle in pulling the front limb backwards and towards 

 the body, as happens while burrowing. These two chest-muscles 

 are probably put to a greater use in this toad at the expense of 

 the sterno-radicdis and the deltoideios. 



