614 



REPTILIA. 



N.S. 



P.A. 



there are horny epidermic scales like those in other Reptiles. The hide 

 is often used as leather. 



The vertebral column consists of distinct cervical, dorsal, lumbar, 

 sacral, and caudal vertebrae, all procoelous except the first two cervicals, 

 the two sacrals, and the first caudal. In most of the pre-cretaceous 

 Crocodilians, however, the vertebrae were amphicoelous. The centra of 

 the vertebrae are united by fibro-cartilages, and the sutures between the 

 neural arch and the centrum persist at least for a long time. Chevron 

 bones are formed beneath the centra of many of the caudal vertebrce. 



Many of the ribs have 

 two heads capitulum 

 and tubercle by which 

 they articulate with the 

 vertebrae. From seven 

 to nine of the anterior 

 dorsal ribs are connected 

 with the sternum by 

 sternal ribs, and from 

 several of these anterior 

 ribs cartilaginous or par- 

 tially ossified uncinate 

 processes project back- 

 wards. The so-called 

 abdominal ribs have 

 nothing to do with ribs, 

 but are ossifications in 

 the fibrous tissue which 

 lies under the skin and 

 above the muscles. They 

 form seven transverse 

 series, each composed of 

 several ossicles. 



As to the skull, there 

 is an interorbital septum 

 with large alisphenoids ; 

 the presphenoid and or- 

 bitosphenoids are at best 

 incompletely ossified ; 

 all the bones are firmly 

 united by persistent 

 sutures ; both upper 

 and lower temporal arcades are completely ossified ; the maxillre, the 

 palatines, and the pterygoid meet in the middle line of the roof of 

 the mouth, covering the vomers, and determining the position of the 

 posterior nares at the very back of the mouth ; an os transversum or 

 transpalatine extends between the maxilla and the junction of palatine 

 and pterygoid ; a postorbital rod (epipterygoid or columella) is 

 formed by a downward process of the postfrontal meeting an upward 

 process from the jugal ; the quadrate is large and immovable ; there 

 are large parotic processes ; the tympanic cavity is completely bounded 

 by bone ; the teeth, which are borne by premaxillre, maxilliv, and 



FIG. 302. Cervical vertebra of crocodile. 



JV.S., Neural spine ; P. A., posterior articular pro- 

 cess ; A. A., anterior articular process; C.R., 

 cervical rib ; C., procoelous centrum. 



