triangle is the longest, and also the broadest ; it is convex in tho antcro-posterior direction, 

 and flat from aide to aide. It i on this lower surface that the teeth are implanted, anil in 

 moat specie* they form two rows ; thr outer one consisting of very small tcrth, the inner onr 

 of large teeth. These present the form of compre*scd conical plates or wedges, witlAhe basis 

 excavated, and the opposite margin moderately sharp and (lightly 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 approximation, one behind another 

 their internal angles are produced beyond the margin of the bone, nnd interlock with those 

 of the adjoining bone when the pharyngeals are in their natural position ; the smaller dcn- 

 ticles of the outer row are set in the external interspaces of those of the inner row. The 

 tingle inferior pharyngeal bone consists principally of an oblong dentigcrous plate ; its breadth 

 somewhat exceeds that of the conjoined dentigerons surfaces of the superior pharyngeals, and 

 it is excavated to correspond with their convexity. The lower dentigcrous plate is princi- 

 pally supported by a strong, slightly-curved, transverse caseous bar, the extremities of which 

 expand into thick obtuse processes for the implantation of the triturating muscles. A longi- 

 tudinal crest is continued downwards and forwards from the middle line of the inferior pha- 

 ryngeal plate, anterior to the transverse bar, to which the protractor muscles are attached. 

 A longitudinal row of small oval teeth, alternating with the large lamclliform teeth like then 

 of the superior pharyngeals, bounds the dentigerous plate on each side ; the intermediate 

 space is occupied by the larger lamelliform or wedge-shaped teeth, set vertically in the bone, 

 and arranged transversely in alternate and pretty close-set series. 



Mwt. Brit. 



131. The inferior pharyngeal bone and teeth, with the dentigcrous portions of the 

 superior pharyngeal bones, of a large species of Scant*, showing the interlock- 

 ing of the superior pharyngeal teeth with each other. Huntcria*. 



182. The inferior pharyngeal bone and a vertical section of one of the superior pha- 

 ryngeals, of a large species of Scanu. The back part of the inferior pharyn- 

 geal is turned towards the number on the tablet, and exposes the large denti- 

 parous cavity for the supply of new teeth to replace those that have been worn 

 out in front. 



The pharyngeal denticles are developed in wide and deep cavities in the substance of the 

 posterior part of the lower and of the anterior part of the upper pharyngeal bones. Each 

 denticle is inclosed in its proper capsule, which contains an enamel-forming pulp and a dcn- 

 tinal pulp, in close cohesion with each other and with their common capsule. The teeth 

 exhibit progressive stages of formation as they approach the posterior part of the upper and 

 the anterior part of the lower pharyngeal bones : as their formation advances to completion 

 they become soldered together by ossification of their respective capsules, and soon after- 

 wards are anchylosed by ossification of the base of the dentinal pulp to the pharyngeal bow 



rS 



