550 



REPTILIA. 



its texture is soft and cartilaginous, the caudal portion of the spine 

 prolonged and flexible ; neither are there any external limbs con- 

 nected with the vertebral column, so as to trammel the lateral 

 movements of the tail; and yet in the mature frog (jig. 247) 

 let the reader observe the amazing difference. The head, it is 

 true, still preserves somewhat of the character of that of the fish, 

 especially in the disproportionate developement of the face, when 

 compared with the size of the cranial cavity ; but all the bones of 

 the spine have become consolidated into ten vertebrae, firmly con- 

 nected together by strong articulations, while the flexible tail of 

 the tadpole has become converted into a strong and immoveable os 

 coccygis, composed of a single piece. 



No ribs whatever are met with in the Frog ; and, even in those 

 Amphibia which are Fig. 247. 



possessed of these 

 elements of the ske- 

 leton, they are mere 

 rudiments appended 

 to the extremities of 

 the transverse pro- 

 cesses of the verte- 

 brae. The sternum, 

 however, is largely 

 developed, and gives 

 extensive attachment 

 to the muscles of the 

 abdomen. The an- 

 terior extremities are 



supported by a semicartilaginous zone, in which the three elements 

 of the shoulder the scapula, the clavicle, and the coracoid bone, 

 are distinctly recognisable ; and the bones of the arm, fore-arm, 

 and hand, are very perfectly formed. 



The pelvis is large, and firmly ossified in correspondence with 

 the strength and magnitude of the hinder extremity ; the ossa ilii 

 being articulated to the ends of the transverse processes of the last 

 vertebra, which from this circumstance may be called the sacrum. 

 The tibia and fibula are consolidated into one bone ; while two of 

 the bones of the tarsus, the astragalus and the os calcis, are so 

 excessively elongated, that they might almost be taken for a second 

 tibia and fibula, did not their position indicate their real nature. 



One circumstance is remarkable in the construction of the 



