118 SCAROIDS. 



the dentigerous plate on each side ; the intermediate space is oc- 

 cupied exclusively by the larger lamelliform or wedge-shaped teeth, 

 set vertically in the bone, and arranged transversely in alternate and 

 pretty close-set series. 



The pharyngeal denticles are developed in wide and deep cavities 

 in the substance of the posterior part of the loiver, and of the anterior 

 part of the uppei' pharyngeal bones. Each denticle is inclosed in its 

 proper capsule which contains an enamel-forming pulp and a dentinal 

 pulp, in close cohesion with each other, and with the thin external 

 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 afterwards are anchylosed by ossification of the 

 base of the dentinal pulp to the pharyngeal bone itself. The line of 

 demarcation between the dentified and ossified portions of the pulp 

 is well defined, so that when the pharyngeal bone and teeth are 

 sawn through vertically the fully formed teeth appear as hollow cones, 

 set upon wedges of bone, as shown in PI. 51, fig. 1. 



The dentine of the pharyngeal teeth of the Scarus consists of 

 calcigerous tubes and a clear intermediate substance. The calci- 

 gerous tubes average a diameter of joith of an inch, and are 

 separated by interspaces equal to twice their own diameter. The 

 course of these tubes is shown in PI. 52, fig. 2, b, in which they 

 are exposed by a vertical section through the middle of one of the 

 inferior denticles. They all, on leaving the pulp-cavity, form a 

 curve with the convexity turned towards the base of the tooth, and 

 then bend slightly in the opposite direction ; the sigmoid curve being 

 most marked in the calcigerous tubes at the base of the denticles, 

 whilst those towards the apex become longer and straighter. Besides 

 the primary curvatures exemplified in the figure, each calcigerous 

 tube is minutely undulated ; it dichotomizes three or four times near 

 its termination, sends off many fine lateral branches into the clear 

 uniting substance [Fl. 52, fig. 3), and finally terminates in a series 

 of minute cells and inosculating loops at the line of junction with 

 the enamel. 



