178 THE ANATOMY OF VERTEBRATED ANIMALS. 



The dentary pieces of the two rami of the mandible are 

 represented 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 coimection 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 b 3 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 skele- 

 ton, 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 re- 

 mains distinct. The free ends of the coracoid and precoracoid 

 are usually connected together by a fibro-cartilaginous 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 tfrodela — 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 

 symphj'sis ; and, sometimes, the foramina obturatoria 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 Ghelys, Ghelodina, and some other 

 genera, the ilia unite by synchondrosis, or anchylosis, with the 

 last costal plate, and the pubis and ischium with the xiphister- 

 nal plates, so that the pelvis becomes firmly fixed between the 

 carapace and plastron. 



The proximal row of the tarsal bones consists usually of 

 an astragalus, formed by the union of the tibiale and interme- 

 dium, and of •a.Jibulare or calcaneum. In Chelyclra there is a 



