294 DIGESTIVE ORGANS. [SECT. 1 38. 



upon the walls of the pulp-cavity ; in which latter place the globules fre- 

 quently produce inequalities visible to the naked eye, or even stalactitic 

 formations. The interglobular spaces, which are normal in the developing 

 tooth, contain, during life, no fluid, as might be believed at first sight, but a 

 soft substance with tubes, agreeing with the tooth-cartilage, and formed 

 exactly like dentine, and which, strange as it may appear, offers more re- 

 sistance to hydrochloric acid than the matrix of the true ossified tooth, and 

 on this account can be isolated exactly like the dentinal tubes. In sections, 

 this ' interglobular substance ' generally dries up in such a manner, that a 

 cavity arises which admits air, and it is only then that we can properly speak 

 of interglobular spaces. Many teeth exhibit, it is true, no interglobular 

 substance, but here and there the outlines of dentine-globules in the form of 

 delicate arched lines (Owen's dentinal cells). 



Dentine with Haversian canals, or vaso-dentine, as it is called by Omen, 

 such as occurs in many animals, is very rarely met with in man, and I only 

 know of one case, which was observed by Tomes (1. c), in which the vascular 

 canals were somewhat numerous ; on the other hand, we occasionally see in the 

 dentine, which is formed in cases of obliteration of the pulp-cavity, along with 

 more irregular dentinal tubes, a few Haversian canals and rounded cavities, 

 which look like bone-corpuscles, the osteo-dentine of Owen, as it is called. 



§ 138. The enamel, substantia vitrea covers the crown of the tooth 

 as a connected layer, is thickest upon and in the neighbourhood of 

 the masticating surface, and gradually decreases towards the fangs, 

 till, at last, it terminates in a thin, sometimes sharp, sometimes 

 slightly indented border. It terminates earlier upon the surfaces 

 of the crowns which are directed towards each other, and extends 

 further downwards upon the inner and outer sides. The external sur- 

 face of the enamel appears smooth, but almost always possesses deli- 

 cate, closely approximated, transverse ridges, along with which well 

 pronounced annular swellings may also occur. A delicate pellicle, 

 which was discovered by Nasmyth, and which I will call the 

 cuticle of the enamel, covers it entirely, but is so intimately con- 

 nected with the enamel, that it can only be demonstrated by the 

 employment of hydrochloric acid. The enamel is bluish, in thin 

 sections, translucent, much more brittle and hard than the other 

 substances of the tooth, so that it can scarcely be penetrated by 

 the knife, and emits sparks when struck with steel {Nasmytli). In 

 chemical composition, it may be compared to an osseous substance, 

 containing a minimum of organic matter ; but the organic con- 

 stituent does not belong to the gelatinous tissues, and differs in no 

 respect from the substance of the epithelium. It contains, ac- 

 cording to Bibra — 



