THE REPTILIAN CLASS OF THE HOSASAURID^l. 697 



These bones (ib. 20) are edentulous. Each sends forward a slender 

 process, a, to join the vomer ; and the junction with the maxillary 

 commences by a similar but shorter process. Between the two 

 processes the fore part of the palatine is deeply emarginate to form 

 the hind boundary of the palato-naris, n. The palatines do not join 

 each other mesially ; the intervomerine fissure is continued back- 

 ward between them, as in the Monitor. In Iguana luberculata * 

 there is no intervomerine fissure ; and a small interpalatine one is 

 insulated from the interpterygoid fissure, s, by a second median 

 suture continued to the junction with the pterygoids. 



In the Amblyrhynchus cristatus it is interesting to find the 

 linear fissure between the hind ends of the vomers (13) continued 

 between the fore ends of the palatines (20), and thence gradually 

 expanding to be continued into the interpterygoid vacuity. Thus 

 the common median fissure, m s, shown in the Monitor and Mosasaur, 

 fig. 16, is repeated in the marine Iguanian. 



But here the palatal correspondence between the small existing 

 and great extinct Lacertians ceases. The pterygoids, in Mosasaurus, 

 (fig. 16, 24), approximate not far from their separate anterior 

 beginnings, unite in the mid line and so close the interpterygoid 

 part of the common fissure, s m ; and this union continues to near 

 the hind end of the dentigerous plate, where the pterygoids again 

 recede to send off the long divergent processes, t, to abut against 

 the tympanic. The number of teeth is 9 or 10 in each pterygoid. 

 The processes for junction with the ectopterygoid and the pterapo- 

 physis of the basisphenoid are well shown in the outer and inner 

 side views of the well-preserved pterygoid bones of the type skull 

 figured by Cuvierf . But there is one significant connexion with 

 an adjacent and peculiarly lacertian bone, shown in the Mosasaurus 

 Maximiliani (fig. 18), which I will illustrate by a corresponding 

 view of the skull of Amblyrhynchus cristatus (fig. 19). 



In this figure, on the upper and outer surface of the pterygoid, 

 24, about midway between the two ends of the bone, there is a low 

 eminence, oc, excavated by a shallow pit in which is lodged the 

 peculiar lacertian bone denominated, from its shaj3e, " columella ;" 

 the upper end of this slender straight vertical pillar (fig. 19, y) 

 abuts against and is firmly attached to the orbitosphenoid, or 

 anterior continuation of the alisphenoidj. 



In the skull of Mosasaurus Maximiliani (fig. 18) a corresponding 

 view of the pterygoid (ib. 24) shows the base of a slender, but 

 broken, vertical pillar, ?/, ankylosed to a similar articular eminence, #. 

 The " columella " of Cuvier is wanting in Ophiclia, as in Chelonia 

 and Crocodilia. 



In general shape and proportions the pterygoid of Mosasaurus 

 more resembles the pterygoid of Hydrosaurus than of Amblyrhynchus, 

 but differs in the dentigerous character, in which the recent Sea- 



* Ouv., torn. cit. pi. xviii. fig. 2, B. 

 t Tom. cit. pi. xviii. fig. 1, k, I, m. 

 \ Cuv., he. cit. 



