REPTILIA. 549 



The Sphenoid, which in Man is regarded as a single bone, is 

 here represented by several distinct parts. The body is divided 

 into two portions {fig. 246, A, 6), called respectively the Anterior 

 and the Posterior Sphenoids. The great or Temporal Ala (11) 

 are also separate bones, as also are the Internal Pterygoids (25). 



A bone (24), which is not met with either in Mammalia or 

 Birds, passes from the Internal Pterygoid to the point of junction 

 between the Zygomatic, the Maxillary, and the Posterior Fron- 

 tal : this has been named by Cuvier the Transverse bone. 



The Ethmoid and the Vomer (16) are but very imperfectly 

 ossified, so that the septum between the nostrils is in the skeleton 

 extremely incomplete, and the sense of smell of course propor- 

 tionately obtuse. 



But the most interesting of the cranial bones is the Tem- 

 poral, which, although considered as one bone by the human osteo- 

 logist, is in Reptiles evidently composed of at least four distinct 

 and separate parts. These are, 1st, the Petrous bone (fig. 246, 

 A, e), which partially encloses the organ of hearing ; 2dly, the Tym- 

 panic bone (a), which supports the membrana tympani ; 3dly, the 

 Mastoid bone (12), which is the homologue of the Mastoid process 

 of Man ; and 4thly, the Temporal bone, properly so called (23), 

 which represents the squamous portion of the human Temporal 

 bone. 



(602.) Each lateral division of the inferior maxilla of Reptiles 

 is separable into at least five and generally six pieces, which are 

 united together by suture; these are named the dental (84), which 

 support the teeth, the angular (36), the opercular (37), the arti- 

 cular (35), and two small pieces seen upon the inner surface of the 

 jaw. 



Having thus described at some length the composition of the 

 skeleton in the Crocodile, which we have chosen for minute ana- 

 lysis, as being the type of the Saurian Reptiles, we shall now pro- 

 ceed to examine the osteology of the other orders, so as to appre- 

 ciate more correctly the peculiarities of structure that they indivi- 

 dually exhibit. 



(603.) In the AMPHIBIA, as for example in the Frog, one of 

 the most striking circumstances connected with their history is the 

 extraordinary change which takes place in the condition of every 

 part of the framework of the body during the evolution of the tad- 

 pole, and its metamorphosis into the perfect frog. 



The skeleton of a Tadpole is, in every particular, that of a fish : 



