SCAROIDS. 117 



pair of the upper pharyngeals which are thus armed ; the lower 

 pharyngeal bone is single. (1) 



The superior dentigerous pharyngeals present the form of an elon- 

 gated, vertical, inequilateral triangular plate ; the upper and posterior 

 margin is sharp and concave ; the upper and anterior margin forms 

 a thickened articular surface, convex from side to side, and playing in 

 a corresponding groove or concavity upon the base of the skull ; the 

 inferior boundary of the triangle is the longest, and also the broadest ; 

 it is convex in the antero-posterior direction and flat from side to 

 side. It is on this surface that the teeth are implanted, and in most 

 ^species they form two rows ; the outer one consisting of very small 

 teeth, the inner one of large teeth. These present the form of com- 

 pressed conical plates or wedges, with the basis excavated and the 

 opposite margin moderately sharp, and slightly convex to near the 

 inner angle which is produced into a point : these plates are set nearly 

 transversely across the lower surface of the pharyngeal bone, and are 

 in close apposition, one behind the other : their internal angles are 

 produced beyond the margin of the bone, and interlock with those of 

 the adjoining bone when the pharyngeals are in their natural position ; 

 the smaller denticles of the outer row are set in the external inter- 

 spaces of those of the inner row, (PI. 51, tig. 2). 



The single inferior pharyngeal bone consists principally of an 

 oblong, dentigerous plate, of the form represented in Plate 51, fig. 3 ; 

 its breadth somewhat exceeds that of the conjoined dentigerous 

 surfaces of the pharyngeals above, and it is excavated to correspond 

 with their convexity. This dentigerous plate is principally supported 

 by a strong, slightly curved, transverse osseous bar, the extremities of 

 which expand into thick obtuse processes for the implantation of 

 the triturating muscles. A longitudinal crest is continued downwards 

 and forwards from the middle line of the inferior pharyngeal plate, 

 anterior to the transverse bar, to which the protractor muscles are 

 attached. 



A longitudinal row of small oval teeth alternating with the 

 large lamelliform teeth, like those of the superior pharyngeals, bounds 



(1) Cheselden has given a ligure of this bone at the end of the first chapter of his 

 " Osteography." 



