332 CLASS REPTILIA. 



ilium is more erect than in that group. There are five digits on 

 each limb. 



The tympanic membrane is not visible externally, but on 

 removing the skin in the aural region there is found a strong 

 aponeurotic expansion which represents it. The tympanic 

 cavity is represented by a large pharyngeal recess. The hyoid 

 arch is continuous with the outer cartilaginous end (extra- 

 stapedial) of the columella,* which is in contact with the parotic 

 process of the skull. It would thus appear that the extra- 

 stapedial cartilage in Sphenodon is the proximal end of the 

 hyoid arch. In their internal anatomy generally they resemble 

 lizards, the most important difference being the absence of 

 co.pulatory organs. The anus is a transverse cleft as in snakes 

 and lizards. The parietal organ is well developed (Figs. 178, 

 189, and p. 344). 



Sphenodon was formerly common on the main islands of New 

 Zealand, but is now restricted to some small islets in the Bay 

 of Plenty. It appears to be on the verge of extinction. The 

 animals inhabit burrows and are nocturnal in habit. They are 

 carnivorous and as a rule slow in their movements. They can 

 however run fast and can defend themselves with some vigour. 

 They lay eggs from November to February. Though the young 

 appear to be almost fully developed in August, they do not 

 hatch out until thirteen months after oviposition. 



There can be little doubt that the Rhynchocephalia are more closely allied 

 to the Lacertilia than to other living reptiles. This is shown by the general 

 form of the body, the presence of a parietal organ, the structure of the 

 respiratory organs, of the vascular system, and by the internal anatomy 

 generally ; and on the whole by the skeletal system. There are however 

 importa,nt points of difference. The most noteworthy of these are the 

 form of the palate (particularly the apposition of the pterygoids), the 

 immoveability of the quadrats, the presence of a lower temporal arcade 

 in the skull ; the erect ilium and the presence of uncinate processes and 

 abdominal ribs. In these features they may be said to approach the 

 Crocodilia, and in some of them the Dinosauria. and Chelonia. The 

 amphicoelous character of the vertebrae is found again in the Geckos, but 

 the absence of copulatory organs is a unique feature a,mong reptiles : on 

 the whole it seems advisable in the present state of knowledge to associate 

 them as was done by Giinther and Huxley with the Laccrlilia and Ophidia, 

 but it must not be forgotten that they do present certain skeletal features 

 which are not present in lacertilians, but which are found in othe^ reptilian 

 groups, particularly in crocodiles. 



* Huxley, P.Z.S., 1869, p. 391. 



