160 EEPTILIA class in 



powerful teeth on either side, and the pterygoids support about eight smaller 



Fig. 252. 



Mosasaurus camperi, v. Meyer. Upper Cretaceous ; Maestricht, Holland. 

 Skull, lateral aspect, Via (after Uollo). 



teeth, all with anterior and posterior carinae. Upper Cretaceous ; Holland, 

 Belgium, France, Northern Germany, and the United States. 



[The text for the preceding chapter on Pythonomorpha has been revised and modified in 

 accordance with the latest researches by Dr. S. W. Williston, Professor of Geology and 

 Palaeontology in the University of Kansas, at Lawrence. — Editok.] 



Sub-Order 3. LACERTILLA Saurii. Lizards. 1 



Scali/, long - failed reptiles, with elongated and sometimes serpentiform body. 

 Superior temporal arcade often wanting, and quadrate loosely attached to the cranium. 

 Columella rod-like or rudimentary ; alisphenoid and orbit osphenoid not ossified. 

 Mandibular rami suturally united at symphysis; teeth acrodont or pleurodonf. 

 Sternum usually, and limb girdles ahvays present, but one or both pairs of appendages 

 sometimes wanting. Limbs ambulatory, and usually provided with five clawed digits. 



The majority of lizards possess a dermal covering of corneous or in some 

 cases of osseous scales, scutes, or spines, extending over the head and whole of 

 the body. The vertebral column consists of numerous procoelous vertebrae 

 (amphicoelous only among the Geckonidae and Uropeltidae), in which the neural 

 arches are thoroughly coossified with their centra. There are seldom more 

 than nine cervicals, and the atlas is composed of two dorsal pieces, either 

 separate or united, and one ventral piece in the form of a free hypapophysis 

 or intercentrum. Both the cervical and dorsal series have the transverse pro- 

 cesses weakly developed, so that the ribs appear attached by a short tubercle. 

 All of the ribs are single-headed. They are wanting on the anterior cervicals, 

 some of the lumbar, and all of the caudal vertebrae. The sacrum is composed 

 of two vertebrae. Stout transverse processes and chevron bones are borne by 

 the caudals. 



A sternum is present, although sometimes rudimentary, in all lizards 

 except Amphisbaena ; it usually occurs as a large rhombic or shield-shaped 

 bone, sometimes pierced by two foramina. The ventral portion of the anterior 



1 Literature : 



Cope, E. I)., The Vertebrata of the Tertiary Formations of the West (Rept. N.S. Geol. Surv. 

 Territ. vol. III.), 1883. — Marsh, 0. ft, On Glyptosaurus, Tinosaurus, etc. (Amer. Journ. Sci. [3], 

 vol. I. p. 456), 1871; and ibid. vol. IV. (1872), p. 298. — Meyer, H. con, Lacerten aus der 

 Braunkohle des Siebengebirges (Palaeoutogr. vol. VII. p. 74), 1860. — Parker, W. K., On the 

 structure and development of the skull in the Lacertilia (Phil. Trans, vol. CLXX. ), 1880. 



