'46 



J. W. HULKE ON AN OS ARTICI7LARE, 



Fig. 3. — Inner View. 



a. Tympanic surface. c. Ascending process. 



Fig. 4. — Under Surface. 





a. Under surface of articular face. b. Outer surface. 



c. Sutural surface for angular bone. 



This foramen is present in all Mr. Fox's specimens, and may be looked 

 on as constant in this type of articular bone. I find it also in the 

 Hypsiloplio don's mandible. A perforation in a bony element, and 

 not a space between the angular, surangular, and dentary pieces, 

 this foramen does not correspond to the large oval opening in the 

 mandible of extant and extinct crocodilians, but rather to the fora- 

 men, sometimes double, present in the surangular element in some 

 extant lizards. (Such foramina are to be seen in Iguana tuberculata, 

 672 a, and Sphenodon, 662 a, Mus. Roy. Coll. Surg.) 



In its whole preserved extent the upper border of the vertical 

 plate is a thin, non-articular, smooth, rounded lip. From in front 

 it gradually and gently rises to a short distance behind the large 

 foramen just described, where it reaches its greatest height ; and 

 thence it descends in a sinuous S- curve, the first bend of which is 

 steep and abrupt, the second bend shallow and open. In front of 

 the tympanic joint the whole inner surface of the vertical plate is 

 non-articular, but less smooth than the outer surface of the same 

 part. It is much hidden by the sheet rising from the front of the 

 tympanic surface, with which it forms the sides of a large and deep 

 hollow, in the fresh state presumably filled with the persistent 



