THE KEPTIL1AN CLASS OE THE H0SASATJRLD.2E. 685 



broad longitudinally, and come off from the antero-lateral parts of 

 the basisphenoid, leaving a wide intervening smooth tract ; the sur- 

 face abutting upon the pterygoid is vertical. 



In Python the pterapopbyses are much shorter, are narrow longi- 

 tudinally, broad transversely, with the surfaces on which the ptery- 

 goids glide horizontal ; they are also close together, divided by the 

 vertical hypapophysial crest. Mosasaurus agrees with the Lacertilia, 

 and differs from the Ophidia in these parts also of the basi- 

 sphenoid. 



Cuvier, in his otherwise full and accurate illustrations of the 

 craniology of Reptilia, gives views of the occipital surface of the 

 skull in Crocodilia * and Chelonia f, but not in Lacertilia. Ophidian 

 remains not having come under his personal cognizance at the date 

 of the preparation of the great work on Fossil Bones, he does not 

 enter into decriptions of the osteology of that order of Reptiles. 

 In that of the other orders he defines and names the bones which 

 contribute to form the otocrane, which he calls " la cage du laby- 

 rinthe " J. In the present inquiry I continue to use these names as 

 most clearly defining the bones I have to refer to. 



In the occipital region of a reptilian skull they are best shown in 

 a Chelonian. In fig. 1 the basioccipital is marked 1, the exoccipital 



Fig. 1. 



Chelonian. 

 Occipital region of skull. 



(" occipital lateral," Cuv.) 2, the paroccipital (" occipital exterieur," 

 Cuv.)§ 4, the superoccipital (" occipital superieur" Cuv.) 3; to these 

 add the parietals 7, with the lateral extensions 7', the squamosal 27, 

 and the mastoid 8 : the proximal part of the " tympanic " is indicated 

 at 28. 



In the Lacertian order I select the skull of the sea-Lizard of the 

 Galapagos Islands (Amblyrhynchus cristatus) for the present aim 

 (fig. 2.) The chief modifications are (the suture between 2 and 4 

 being obliterated) : — the greater extension of the transverse abut- 

 ment, 2-4, against the joint contributed by the mastoid, 8, and squa- 



* Tom. cU. pi. iii. fig. 5. f Ibid. pi. xi. fig. 4. \ Tom. cit. p. 181. 

 § "Les occipitaux lateraux sont chacun divises en deux parties, dont je me 

 vois oblige d'appeler la plus externe occipital exterieur." (lb. p. 180.) 



