32 PACHYDERMATA. 



capsule, which is lodged in a cavity of the maxillary bone, 

 and which forms the mould, so to speak, of the tooth. The 

 exterior of this sac is simple, while its internal surface is expanded 

 into numerous folds, which determine the arrangement of the 

 'ivory,' 'enamel,' and 'cement,' entering into the composition 

 of the tooth. From the bottom of the sac a gelatinous mass, 

 the 'pulp nucleus,' is projected upwards, subdivided into trans- 

 verse digitated plates or segments, varying in number, length, 

 and thickness in different species, and more or less numerous in 

 different molars of the same individual, according to the age of 

 the tooth. These ' pulp ' segments are attached only by their 

 base, and attenuate gradually upwards to their summits, being 

 entirely free from adhesion, either to the opposite side of the 

 sac, or to the contiguous ' pulp ' divisions. The ossification of 

 this 'pulp nucleus,' by the deposition of calcareous matter within 

 the cells of its tissue, constitutes the ivory core, or central part of 

 the tooth, being the substance called ' dentine ' by Professor 

 Owen. 



From the opposite or coronal side of the capsule, other folds or 

 induplications are given off, which proceed into the spaces between 

 the divisions of the 'pulp nucleus.' Their attachment is continued 

 along the parietes of the sac, so that on every side, except the 

 base, they envelope the processes of the 'pulp nucleus,' over which 

 they are closely applied, interlocking with the latter ; the two 

 sets of processes thus forming productions from the interior of the 

 sac which are opposed to each other in the manner of salient 

 and re-entering angles. The ossification of these peripheral 

 folds in a continuous surface constitutes the - enamel,' or vitreous 

 shell, which encloses the ivory core of the crown of the teeth, 

 terminating abruptly where the fangs commence. 



Exterior to, and following the folds of this ' enamel pulp,' there 

 is another modification of the internal membrane of the sac, the 

 ossification of which, during the last stage of the development of 

 the tooth, constitutes t the external 'cortical layer,' or 'cement,' 

 which, in a crust of greater or less thickness, is continued over the 

 enamel of the crown, and down upon the fangs. In the true 



