REPTILIA. OPH1DIA. 203 



elongated body and want of limbs. The body is covered with 

 overlapping horny scales and bony dermal scutes are never 

 present. The vertebrae are precocious, and are distinguishable 

 into two groups only, precaudal or rib-bearing, and caudal or 

 ribless. The atlas vertebra is also ribless. The neural arches 

 are always provided with zygospheiies and zygantra. Many 

 of the vertebrae have strong hypapophyses, and the caudal 

 vertebrae are without chevron bones. 



In the skull the cranial cavity extends forwards between 

 the orbits, and is closed in front by downgrowths from the 

 f rontals and parietals which meet the well-ossified alisphenoids 

 and orbitosphenoids 1 . The cranium is strongly ossified, and 

 there are no parotic processes or interparietal foramen. There 

 are no temporal arcades and no epipterygoid. The premaxillae 

 if present are very small (fig. 51, 1) and usually toothless. 

 The quadrates articulate with the squamosals, and do not as 

 in Lacertilia meet the exoccipitals. The palatines do not 

 unite directly with the vomers or with the base of the cranium, 

 and the whole pala to-maxillary apparatus is more loosely con- 

 nected with the cranium than it is in Lacertilia. The ptery- 

 goids, and in most cases also the palatines, bear teeth. The 

 dentition is acrodont, and the rami of the mandible are united 

 only by an elastic ligament an important point serving to 

 distinguish the Ophidia from the Lacertilia. There is an 

 imperfectly developed interorbital septum, the ventral part 

 of which is formed by the paraspherioid. The postfrontal is 

 generally well developed, while the jugals and quadratojugals 

 are absent. There are never any traces of the anterior limbs 

 or pectoral girdle, but occasionally there are vestiges of a 

 pelvis and posterior limbs. 



1 Some anatomists consider that the closing in of the brain case in 

 front is entirely due to the frontals and parietals. 



