206 THE ANATOMY OF VERTEBEATED ANIMALS. 



The dentary pieces of the two rami of the mandible are 

 reiDresented by one bone, as in Birds. 



The hyoidean apparatus consists of a broad plate of car- 

 tilage with two longer anterior, and two shorter posterior, 

 ossified cornua. The cornua have no direct connection 

 with the skull. 



The pectoral and pelvic arches appear, at first sight, to 

 have a very anomalous position in the Chelonia, inasmuch 

 as they seem to be situated inside, and not outside, the 

 skeleton of the trunk. But since the plastron does not 

 answer to the sternum of other Vertebrata, but to part of 

 the dermal skeleton, the anomaly does not really exist on the 

 ventral side. And, as to the dorsal side, the pectoral and 

 pelvic arches of the fcetal Chelonian are at first situated in 

 front of, or behind, and external to, the ribs, as in other 

 Vertebrata. It is only as development advances, that the 

 first costal plate extends over the scapula, and the hinder 

 costal plates over the ilium. 



The pectoral arch is ossified in such a manner that the 

 scapula and precoracoid form one bone, while the coracoid 

 remains distinct. The free ends of the coracoid and pre- 

 coracoid are usually connected together by a fibro-carti- 

 laginous band, representing the epicoracoidal cartilage in 

 Lacertilia. There is no clavicle, unless the epiplastra and 

 entoplastron represent that bone. 



The carpus of the Chelonia contains nine primary ossicles, 

 as in the Urodela — three in the proximal row, one central, 

 and five distal — and these almost always remain distinct. 



There are five digits, the numbers of the phalanges of 

 which present no constancy. 



The pelvis contains the usual bones. The pubes (which 

 are very large) and the ischia meet respectively in a long 

 symphysis ; and, sometimes, the foramina obttiratoria are 

 completed, internally, by the meeting of the bony pubes and 

 ischium of each side in the middle line. 



The pelvis is not usually united with either the carapace 

 or the plastron, but in Chelys, Chelodina, and some other 



