084 



CLASS REPTILIA. 



no trace of a sternum. In the plastron (fig. 1009), developed on 

 the ventral aspect, the epiplastrals (es) and entoplastral (s) corre- 

 spond to the three plates of the Labyrinthodont thoracic buckler, 



Fig. 1007. — Left lateral aspect of the skull of Testudo. j>m, Premaxilla ; m, Maxilla; pf, 

 Prefrontal and nasal ; f, Frontal ; p, Parietal ; o, Supraoccipital ; z, Jugal, behind which is the 

 quadratojugal, and above the postfrontal ; t, Quadrate, showing the incompleteness of the tym- 

 panic ring posteriory ; the bone above this ring is the squamosal. 



and apparently represent the clavicles and interclavicle. There 

 are in addition paired hyo-, hypo-, and xiphiplastrals ; and in some 

 forms (fig. 10 1 2) there are mesoplastrals 

 intercalated between the hyo- and hypo- 

 plastrals. The pelvic, like the pectoral 

 girdle, becomes in the adult placed on 

 the inner side of the ribs, and has the 

 pubis much larger than the ischium (fig. 

 1006). The two latter may be anchylosed 

 to the xiphiplastral, and the obturator 

 notch may be converted into a foramen. 

 The humerus has an ectepicondylar groove, 

 which is occasionally converted into a fora- 

 men. There is a centrale in the carpus 

 (fig. 829), and in the Chelydrida also in 

 the tarsus. The tarsus may probably be 

 regarded as having five distinct tarsalia, 

 as in the Amphibia and Mesosaurus. In 

 both the manus and pes there are always 

 five digits, with a variable number of 

 phalangeals. Not unfrequently the bones of the palate develop 

 inferior plates to floor the nasal passage, and thus produce second- 

 ary posterior nares with a vertical aperture. Since the palaeonto- 



Fig. ico8.— Right side of the 

 pectoral girdle of Testudo. s, 

 Scapula ; a, Precoracoid ; c, 

 Coracoid. 



