196 THE ANATOMY OF VERTEBRATED ANIMALS. 



the middle of the tail, have the ordinary structure ; but bej'ond 

 this point they bifurcate, so that each vertebra seems to have two 

 spinous processes, a peculiarity unknown in other Lacertilia. 



The laro-e chevron-bones are articulated between the bod- 

 ies of the caudal vertebrae, as in the Crocodllia^ but also as in 

 some LacertlUa^ such as the Geckos. The skull is preserved 

 in one specimen only, and in that it is in such an imperfect 

 condition that the details of its structure cannot be made out. 

 The teeth, however, are nearly straight, conical, and sharply 

 pointed, and seem to have been implanted in distinct sockets, 

 though there may be some doubt upon this point. 



The pectoral and pelvic arches are large and strong. The 

 fore-limbs are shorter than the hind-limbs, and each limb 

 bears five digits. The manus contains certainly eight, possi- 

 bly nine, carpal bones, five of which correspond with the meta- 

 carpals. The number of phalanges is exactly the same as in 

 most existing Lacertilia (2, 3, 4, 5, 3). In the pes, again, the 

 number of the phalanges is characteristically Lacertilian (2, 3j 

 4, 5, 4), and so is the form of the fifth metatarsal, but the two 

 proximal tarsal bones appear to have been less closely connect- 

 ed together than in existing Lacertilia^ and there were, at 

 fewest, three distal tarsal bones with w^hich the metatarsals 

 articulated, and by which they were completely separated 

 from the proximal tarsals. Among existing Lacertilia an ar- 

 rangement similar to this is met with only in the Ascalabota. 



5-9. The great majority of existing Lacertilia belong to 

 the procoelous Kionocrania,, with not more than nine cervical 

 vertebrae, and they deviate but little in their osteology from 

 the general type of organization which has been described. 



The skull in the Platynota^ or Monitors of the Old World, 

 with the American genus Heloderraa^ differs from that of any 

 other Lacertilia in the circumstance that the nasal bones are 

 represented by a single narrow ossification. 



In the genus Lacerta the bones of the roof of the skull 

 become continued into dermal ossifications, which roof over 

 the supra-temporal fossas. In the Chalcidea and Scincoidea, 

 in which the body sometimes becomes elongated and snake- 

 like, and the limbs rudimentary, the supra- and infra-temporal 

 arcades are apt to be ligamentous, and the post-frontals and 

 squamosals small. 



10. The Dolicliosauria. — A very singular Lacertilian found 

 in the Chalk, and resembling an eel in form and size, has been 



