484 Comparative Morphology of Chordates 



classed as separate orders or as subdivisions of one. Crocodilians and 

 turtles obviously represent separate orders. Aside from the four types 

 just mentioned, only one modern reptile type remains — the New Zea- 

 land tuatara. The following arrangement makes five orders of existing 

 reptiles. 



Order Rhynchocephalia 



Sphenodon. Vertebrae with amphicoelous centra perforated 

 (at least in younger individuals) by the persisting notochord, 

 which is continuous but constricted by each centrum. Skull resembles 

 I hat of early reptiles and differs from I hat of lizards in many particulars 

 — most notably in that the quadrate (the upper jawbone to which 

 the lower jaw is articulated) is immovably joined to adjacent bones 

 of upper jaw and cranium (Fig. 373). Legs well developed. Ribs have 

 uncinate processes (Fig. 363). Sternum and gastralia ("abdominal 

 ribs") are present. Median dorsal parietal eye especially well devel- 

 oped. Cloacal aperture is a transverse slit. Large urinary bladder. 

 Oviparous. 



The only living member of the order is the tuatara, Sphenodon 

 (Hatteria) punctatum, found only in New Zealand (Fig. 374). 

 Externally resembling a lizard (length 18 inches or more), the animal's 

 internal peculiarities forbid classifying it with lizards and identify it 

 as the sole survivor of one of the most ancient and once widespread 

 orders of reptiles. Sometimes spoken of as a "living fossil," it is of such 

 great scientific importance that, in the hope of preventing its untimely 

 extinction, it has been protected by legislation prohibiting its capture 

 except for scientific purposes. 



SUPERORDER SQUAMATA 



Lizards and Snakes. Quadrate bone more or less elongated; its 

 dorsal end movably (except in chameleons) joined to adjacent bones 

 of the otic region of the cranium. Thus, between lower jaw and 

 brain-case, two joints intervene — an arrangement giving greater 

 freedom to the movement of the lower jaw and increasing the extent 

 to which the mouth may be opened (Fig. 375). Cloacal aperture is a 

 transverse slit. 



Order Sauria (Lacertilia) 



Lizards. Notochord not persistent and vertebral centra usually 

 procoelous, except in the geckos, whose vertebrae resemble those of 

 Sphenodon. Pectoral and pelvic legs usually strongly developed 

 (Fig. 376). Sternum usually present; several pairs of anterior "tho- 

 racic" ribs attached to it. Gastralia rarely present: they occur in 

 "monitors" (Varanus) and in some others. Movable eyelids, the 



