REPTILTA. 553 



bands, and even the arches of the palate are moveable. The 

 two halves 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 connection 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 sur- 

 prising manner, and prey of apparently very disproportionate bulk 

 thus introduced into the stomach. 



(607.) The most extraordinary skeleton met with among Rep- 

 tiles, 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 

 Plastrum, between which the limbs and the head can be more or 

 less completely retracted. 



Yet, notwithstanding this apparent total inversion of the osseous 

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

 what slight modifications in the arrangement of the elements of the 

 skeleton such prodigious changes are accomplished. This is well 

 exemplified in the construction of the Carapax of the common Tor- 

 toise (EmysEuropaus). In this well-known animal (Jig. 250) the 

 vertebrae of the neck, and of the tail, present nothing particu- 

 larly remarkable in their structure ; but, being connected together 

 in the ordinary manner, the neck and caudal region of the spine 

 present their usual flexibility. The dorsal vertebrae, however, are 

 strangely distorted ; the elements of the upper arch being dispropor- 

 tionately developed, while the bodies remain almost in a rudimen- 

 tary condition. The superior spinous processes of these vertebras 

 are flattened, and converted into broad osseous plates, which form a 

 longitudinal series along the centre of the back, and are connected 

 together by sutures resembling those of the human cranium. The 

 ribs are changed into broad flat bones, firmly united by suture to 

 each other, and also to the lateral margins of the spinous processes 

 of the vertebrae, so that they all form, as it were, a single broad 

 plate : the heads of the ribs are very feebly developed, and the 

 intervals 'between them and the bodies of the vertebrae filled up 

 with ligament. The margin of the shield thus formed by the dorsal 

 ribs is further enlarged by a third set of flat bones, apparently 

 representing the sternal ribs of the Crocodile, fixed by suture 



