OSTEOLOGY OF AMPHIBIAN REPTILES. 679 



(1893.) 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 (6), called respectively the anterior and the posterior sphenoids. 

 The great or temporal alee (ll) are also separate bones, as also are the 

 internal pterygoids (25). 



(1894.) A bone (24), which is not met with either in Mammalia or 

 Birds, passes from the internal pterygoid to the point of junction be- 

 tween the zygomatic, the maxillary, and the posterior frontal: this has 

 been named by Cuvier the transverse bone. 



(1895.) 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 proportionately 

 obtuse. 



(1896.) But the most interesting of the cranial bones is the temporal, 

 which, although considered as one bone by the human osteologist, is in 

 Eeptiles evidently composed of at least four distinct and separate parts. 

 These are, 1st, the petrous bone (fig. 332, A, e), which partially encloses 

 the organ of hearing ; 2ndly, the tympanic bone (a), which supports the 

 membrana tympani ; 3rdly, the mastoid bone (12), which is the homo- 

 logue 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. 



(1897.) 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 (34), which support the 

 teeth, the angular (36), the opercular (37), the articular (35), and two 

 small pieces seen upon the inner surface of the jaw. 



(1898.) Having thus described at some length the composition of the 

 skeleton in the Crocodile, which we have chosen for minute analysis, 

 as being the type of the Saurian Reptiles, we shall now proceed to 

 examine the osteology of the other orders, so as to appreciate more 

 correctly the peculiarities of structure that they individually exhibit. 



(1899.) In the AMPHIBIA, as for example in the Frog, one of the 

 most striking circumstances connected with their history is the extra- 

 ordinary change which takes place in the condition of every part of the 

 framework of the body during the evolution of the tadpole and its 

 metamorphosis into the perfect frog. 



(1900.) The skeleton of a Tadpole is, in every particular, that of a 

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

 prolonged and flexible ; neither are there any external limbs connected 

 with the vertebral column, so as to trammel the lateral movements of 

 the tail ; and yet in the mature Frog (fig. 333) 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 de- 

 velopment of the face when compared with the size of the cranial cavity ; 



