OPHTHALMOSAUEUS. 



33 



represents the foramen figured by Gilmore*, but if so it was entirely concealed within 

 the symphysis. The upper border of the bone is rounded and helps to form the inner 

 wall of the posterior part of the alveolar groove. Behind this it thins, and its upper 

 border slopes away till it terminates in a point about the level of the coronoid process. 

 The outer face is applied to the dentary in front, and to the coronoid and angular 

 behind. Ventrally the anterior portion of the bone appears below the dentary and 

 forms the lower edge of the mandible, but farther back it thins out and its lower 

 border slopes up to its posterior termination, the posterior third or so of the bone 

 lying entirely on the inner face of the ramus. 



The surangular {s.cmg., text-figs. 20, 21) forms the upper border of the hinder 

 portion of the mandible. It is a long bone, consisting of a pointed anterior prolonga- 



Text-fig. 21. 



Left surangular bene of Ojphthalmosaurus : A, iuner side ; B, outer side. (R. 2740 about ^ nat. size.) 



ang.f., facet for union with the angular ; art.f., facet for union with the articular bone ; art.s., articular 

 surface; c, c'., coronoid processes ; cor.f., facet for union with the coronoid bone; dent.f,, surfaces of 

 union with the dentary ; foi-., foramen on outer surface of bone ; (j., groove running forwards from 

 the foramen ; t., tubercle at hinder end of articular surface. 



tion and a much broader posterior articular portion. It is partly concealed in front 

 by the overlapping of the dentary, but below this the surface is exposed and bears a 

 very deep longitudinal groove (g.) into which a foramen (for.) opens posteriorly. 

 The inner face of the anterior portion is flattened and covered first by the dentary 

 and behind this by the anterior expansion of the bone here called the coronoid (go7'.) ; 

 this, however, diverges from it posteriorly, and slopes away so that for some distance 

 its inner face is exposed. Behind this point comes the articular bone (art.), closely 

 adherent to the inner face of the surangular. The upper border of the bone is 

 rounded in front, but posteriorly becomes thinner, and is raised into two blunt 

 processes, one directed upwards, the other a little further back directed somewhat 



: * " Notes on Osteology of Bajptanodon," Mem. Carnegie Museum, vol. ii. (1906) p. 327. fig. 1. 



