216 THE ANATOMY OF VEETEBEATED ANIMALS. 



whatsoever that the true posterior nares are situated far 

 forwards, in the position assigned to them in Plesiosaurus. 



The pectoral arch of Nothoscmrus, again, presents a very- 

 interesting deviation from the Plesiosaurian type. The 

 coracoids, indeed, are greatly expanded, and meet by their 

 inner edges, so that the rhomboidal part of the sternum 

 seems to have been wholly absent, and the scapulae have a 

 horizontal prolongation, not quite so long as in Plesio- 

 saurus, with an upstanding proper scapular part of corre- 

 sponding shape. But then the ends of these preglenoidal 

 processes are connected together by, and indeed suturally 

 united with, a stout, curved, transverse bar of bone, con- 

 sisting of three pieces, one small and median, and two very 

 large and lateral, all united firmly together by sutures. 

 There can be little doubt that the constituents of this bony 

 bar correspond with the interclavicles and clavicles of 

 Lacertilia and Ichthyosawria. 



III. The Laceetilia. — Some few Lacertilia, like the Oha- 

 mseleons and the AniphisbcenoB, are covered by a soft integu- 

 ment ; but, in the majority, there is an epidermic exoskeleton 

 composed of horny plates, tubercles, or spines, or over- 

 lapping scales. In some forms (e.g. Scincus, Cyclodus) the 

 dermi beneath the homy scales is ossified, and the body 

 has a complete armour of bony scutes, corresponding in 

 form with the scales. The dermal ossifications of the head 

 may coalesce with the subjacent bones, but this union of 

 dermal bones with subjacent parts does not occur in other 

 parts of the body. 



The spinal column always contains a considerable number 

 of vertebrae ; and, except in the Amphisbcence and some few 

 other Lizards, the tail is long. Those Lizards which possess 

 hind limbs have a sacrum, into which not more than three 

 vertebrae, and rarely more than two, enter. The presacral 

 vertebrae are distinguishable, when sternal ribs are present, 

 into cervical and dorsal. All those vertebrae which lie in 

 front of the first sternal rib are cervical ; and if, as sometimes 

 happens, the last two or three dorsal vertebrae are devoid of 



