682 REPTILIA. 



(1906.) Having already enumerated the bones which enter into the 

 composition of the cranium of a Saurian Reptile, it would be super- 

 fluous again to mention in detail those met with in the skull of a Ser- 

 pent, more especially as they will be easily recognized by a glance at the 

 annexed figure, in which the corresponding bones are all indicated by the 

 same references. One peculiarity only requires special notice, namely 

 the extreme mobility of the principal bones of the face, and more par- 

 ticularly of the pieces composing the lower jaw, by which provision these 

 reptiles are enabled to swallow entire animals of astonishingly large 

 dimensions when compared with the size of their mouth. 



(1907.) In order to allow of this, the bones composing the superior 

 maxilla (fig. 335, 17, 18) are only loosely joined together by ligamentous 

 bands ; and even the arches of the palate are moveable. The two halves 



Skull of Boa. 



of the lower jaw (34, 34) are connected together at the symphysis by a 

 ligament so loose and elastic that separation to a great extent is easily 

 allowed ; and, moreover, those two elements of the temporal, the mastoid 

 (12) and the tympanic (a), which form the bond of connexion between 

 the inferior maxilla and the cranium are here lengthened out into long 

 pedicles, so that by their mobility the entrance to the throat can be 

 dilated in a surprising manner, and prey of apparently very dispropor- 

 tionate bulk thus introduced into the stomach. 



(1908.) The most extraordinary skeleton met with among Reptiles, 

 and, indeed, among the Vertebrata generally, is that of the CHELONIA, in 

 which the ribs and sternum are both placed quite at the exterior of the 

 body, so as to form a broad dorsal shield called the carapax, and an 

 equally strong ventral plate named the plastron, between which the 

 limbs and the head can be more or less completely retracted. 



(1909.) Yet notwithstanding this apparent total inversion of the 

 osseous system in the creatures before us, it is interesting to observe by 



