232 ON THE DEVELOPMENT OF THE TEETH 



tooth-pulp is a dermic process bounded by its basement membrane ; 

 the capsule is an involution of the derm, bounded by its basement 

 membrane ; and the epithelium of these organs lies between them, 

 having in this case received the name of " Enamel-organ," from the 

 supposition that the enamel was developed by the calcification of its 

 elements. Of this, however, I shall speak below. 



There is an important difference between the dental sac of the 

 Calf and that of Man, which has given rise to much confusion. 



The '' actinenchymatous " tissue (Raschkow) of the former does 

 not at all correspond with the stellate tissue of the latter, as has 

 been assumed by all writers. In fact, in the Calf the wall of the 

 capsule is separated by only a very narrow space from the surface 

 of the pulp, and this space is completely filled up by elongated 

 cylindrical epithelium cells, which glue the capsule to the pulp. 

 Between the basement membrane of the capsule and the alveolar wall, 

 indeed, there is a very wide interval (see Owen, /. c, pi. CXXII. a, fig. 

 9 e) occupied by Raschkow's actinenchyma. This, however, is nothing 

 more than a loose submucous cellular tissue of the gum, similar to that 

 so well described by Mr. Nasmyth in the wall of the capsule of man. 

 Professor Owen says (/. c, Introduction, p. lix.) that " no capillaries 

 pass from the capsule into the actinenchymatous pulp of the enamel. 

 But those which I have examined do not bear out this statement ; in 

 fact, this tissue presents one of the most beautiful and obvious vascular 

 networks with which I am acquainted. ^ 



The true homologue of the " enamel organ " in Man therefore, in the 

 Calf, is not the actinenchymatous tissue, but the thin layer of epithe- 

 lium between this and the pulp. The general relations of the different 

 dental organs are in other respects, the same in the Calf as in Man. 



I may now proceed to the second question. What is the relation 

 of the proper dental tissues to the three organs of the tooth capsule ? 



The answer is shortly this. Neither the capsule nor the " Enamel- 

 organ " take any direct share in the development of the dental tissues 

 all three of which — viz., enamel, dentine, and cement — are formed 

 beneath the membrana preformativa, or basement membrane of the 

 pulp. In proof of this assertion, I have to offer the following facts : — 

 If, in the human foetus of the seventh month, a dental capsule (say of 

 an incisor) be treated as I have above described, it will generally 

 happen that the surface of the young tooth-cap appears quite smooth 

 under a low power ; or it may be that a few of the elongated cells of 



^ Blake, who wrote in 1801, mentions the vascularity of the "spongy" outer membrane 

 of the tooth sac in the calf; he says it is "very vascular." — p. 81. 



