OSTEOLOGY OF RHAMPHOCOTTUS 467 



unite with the nasal bone. Posteriorly the bone forks broadly, 

 the wide limbs overlapping the superior surface of the frontals. 

 Distally the bone forks narrowly to each side of the central limb 

 of the vomer (figs. 5 and 6). 



The vomer (v.). The anterior part of the vomer is smooth, 

 wide, and crescent-shaped and from this part a median process 

 extends caudad to articulate with the parasphenoid and the 

 ethmoid. The under edge of the crescentic part is beset with 

 numerous villiform teeth (figs. 5, 6 and 7). 



The nasal (na.) bones are relatively large and bear strongly 

 developed sharp spines. Each has a groove on its anterior sur- 

 face separating it in part from the ethmoid and the prefrontals. 

 This groove forms one margin of the nasal foramen. The outer 

 wing of the nasal articulates with the prefrontal, and the inner 

 process, with the ethmoid (figs. 5 and 6). 



2. Suborbital ring 



The suborbital ring consists of three bones. The anterior or 

 preorbital (por.) is wide and flat, slightly convex externally, and 

 articulates with the prefrontal superiorly and passes down over 

 the side of the snout. The general shape and position of this 

 and the next two bones described are shown in figure 4. The 

 middle member of the suborbital ring, the suborbital (sor.), is a 

 thin, wide bone of irregular outline, also slightly convex exter- 

 nally. The bony stay or postorbital (ptor.) is the third and 

 largest of the bones comprising the suborbital ring. Posteriorly 

 it is somewhat ovoidal in shape and the outer surface is strongly 

 convex. From its articulation with the suborbital anteriorly 

 it passes into the anterior angle of the preoperculum where it is 

 firmly attached (fig. 4). 



3. Suspensorium, mandibles, and opercular apparatus 



The hyomandibular (hm.) is a strong bone of irregular outline. 

 The superior part is expanded to form a large head which articu- 

 lates in a groove just beneath the lateral shelf of the pterotic, on 

 its anterior half, and overlapping slightly the sphenotic bone. 



