16 ODONTORXITHES 



The layer of enamel gradually increases in thickness from the base 

 of the tooth to the apex, as shown in figure 4, a. It is also somewhat 

 thicker over the anterior cutting edge than in other portions of the base 

 of the crown, as indicated in figure 5. The line of junction between the 

 enamel and the dentine is everywhere sharply defined. The enamel is 

 dense and hard, the calcification having proceeded so far, in the specimens 

 examined, that the constituent fibres could not be distinguished. The 

 external surface of the enamel is nearly smooth, but marked by delicate 

 striae. There is no indication of cement on the coronal surfaces. 



The dentine, which forms the mass of the crown, shows a well marked 

 structure in both the vertical and horizontal sections, figures 4 and 5, b. 

 It is firm and compact, and the calcigerous tubes are well defined. Near 

 the base of the crown, they radiate horizontally, and in transverse section 

 appear nearly straight, as shown in figure 5. Higher up in the crown, 

 these tubes curve upward, diverging from the axis of the tooth less and less, 

 until beneath the apex they become nearly parallel. In the dentine, there 

 are distinct concentric lines of growth. These are seen near together and 

 numerous in transverse section, figure 5, while those which appear in the 

 vertical section, figure 4, are fewer in number, and more strongly marked. 



The teeth of Hesperomis, taken by themselves, appear to resemble 

 more nearly the detached teeth of Mosasauroid reptiles, than any others 

 known, not excepting the teeth of Ichthyomis, which will be fully described 

 in a subsequent chapter. The teeth in the latter have compressed crowns, 

 and are implanted in distinct sockets. In all their main features, the teeth 

 of Hesperomis are essentially reptilian, and no anatomist would hesitate 

 to refer them to that class, had they been found alone. Combined with 

 the other reptilian characters of Hesperomis, noted elsewhere in the present 

 volume, they clearly indicate a genetic connection with that group. 



