552 REPTILIA. 



ed ; and, contiguous vertebrse being likewise mo veably connected 

 together by means of these appendages, unnecessary flexure is 

 not allowed, and all danger of dislocation prevented. 



(605.) Serpents, being entirely deprived of external limbs, have 

 neither shoulder nor pelvis ; their ribs alone affording them the 

 means of progression. These extend on each side in an uninter- 

 rupted series from the first vertebra behind the head to the origin 

 of the tail, so that the division of the spine into regions is here out 

 of the question. Every rib (fig. 248, a) is attached at its origin 

 by a kind of ball-and-socket joint to the extremity of the correspond- 

 ing transverse process of a vertebra (6), and is therefore freely move- 

 able. There is no sternum here, neither are there sternal ribs ; but 

 the dorsal ribs, wielded as they are by innumerable and powerful 

 muscles connected with them, literally perform the office of inter- 

 nal legs, and materially assist the creature in progression. 



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

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

 superfluous again to mention in detail those met with in the skull 

 of a serpent, more especially as they will be easily recognised by 

 a glance at the annexed figure, in which the corresponding bones 

 are all indicated by the same references : one peculiarity only re- 



quires special notice, namely, the extreme mobility of the principal 

 bones of the face, and more particularly 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 mouths. 



In order to allow of this, the bones composing the superior 

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



