24 MICROSCOPIC ANATOMY OF THE TEETH 



that the epithelial masses play a certain role in the eruption 

 of the corresponding tooth '. 



These observations will be further considered in treating 

 of the dental follicle (see p. 317), but Warwick James (11) 

 has lately expounded a similar view in connexion with the 

 eruption of the temporary teeth. He considers that the 

 epithelium ' directs the tooth to its position in the gum ', 

 and that the ' path of eruption is prepared by the epi- 

 Epitheliai fchelium '. The principal agents in providing this path are 

 the 'epithelial coils' or 'globes epidermiques ', which, by 

 opening out and disrupting, form spaces in the connective 

 tissue of the follicle in the course of the erupting tooth. 

 The epithelial coils will be further considered in another 

 place (p. 312). 



The tooth-sacs, shown in fig. 5 as they appear at birth, 

 consist of an outer and an inner coat, the outer connected 

 with the periosteum, and the inner coat richly supplied 

 with blood-vessels and separated from the outer by a thin 

 layer of jelly-like connective tissue. The extreme vascularity 

 of the inner coat ' doubtless has relation to the nutrition of 

 the enamel organ ' (Schafer). 



From the tooth-sac, which is seen to take its origin from 

 the tissue of the mesoderm, the cement and periodontal 

 membrane are formed, and in those animals which possess 

 coronal cement, an investing cap of cement also. 



Fig. 5, drawn by the author from a preparation by 

 Professor Symington, shows the tooth- sacs in the left half 

 of the mandible at birth, and in figs. 6 and 7 are shown the 

 stages of calcification of the milk teeth at birth. It is seen 

 that the calcified cusps of the molars have become fused 

 together, and the calcification of the first permanent molar 

 appears as a tiny triangle in its crypt. 



Fig. 8, a skiagram from Professor Symington's atlas (23) y 

 shows very distinctly the stages of calcification at the 

 period of birth. The crypts of the teeth are seen and the 

 fusion of the calcifying cusps of the temporary molars i& 

 well shown, also the single calcified point of one cusp of 

 the first permanent molar. As pointed out by Professor 

 Symington, there is no important difference between this 

 specimen (one month old) and that of the newly-born 



