288 



OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



and thus the dentine with its tubuli are generated. This process progressively 

 extends itself from the surface of the pulp, towards its centre ; for as the more 

 external and larger cells become hardened, the inner ones increase in size, assume 

 the linear arrangement, and in their turn become converted into dentine; until 

 at last the great bulk of the pulp is transformed, leaving only a comparatively 

 small portion, which, with the nerves and bloodvessels, occupies the central 

 cavity of the tooth. In this progressive development, it often happens that two 



Sections of the Dentinal Pulp in successive stages of its development. 



of the more external cells unite with one of the cells next to them on the internal 

 side (Fig. 80, c), their two canals also uniting to form one ; and by the frequent 

 repetition of this process of union it happens, that the number of dentinal tubes 

 gradually diminishes as we pass from the periphery towards the centre. The 

 " nodular layer" (Fig. 76) which commonly exists near the surface of the tooth- 

 fang, and the similar structure which occasionally (though abnormally) presents 

 itself elsewhere, are considered by Mr. Tomes to depend upon the partial con- 

 tinuance of the original areolar structure of the pulp, whilst it is undergoing 

 calcification ; the calcifying process having either commenced at an unusually 

 early period, when as yet the linear arrangement of the cells for the development 

 of the tubular structure has not yet taken place, so that the dentinal substance 

 thus formed has a very imperfect character ; or, in other cases, the space origi- 

 nally occupied by the areolar texture not having been filled up, whilst the cells 

 were undergoing development into tubes, so that vacuities are left, which pre- 

 serve its original form. 1 



280. The Enamel-pulp is not formed until after the dental papilla has become 

 enclosed in a capsule, by the process to be presently described ; and it is derived 

 from the free inner surface of the capsule, of which its cells may be considered 

 as the epithelium. Of this pulp, however, which fills the whole space between 

 the surface of the papilla and the lining of the follicle, only that portion which 

 is immediately adjacent to the former is the actual matrix of the enamel; the 

 remainder serves but a temporary purpose, and afterwards disappears. In its 

 earliest condition, the enamel-pulp, according to Mr. Tomes, bears a strong 

 resemblance to the first stage of the dentinal ; for it consists of a meshwork of 

 very fine fibres (which seem to be composed of the yellow element), whose inter- 

 spaces are occupied by a thick transparent fluid, floating in which are some pecu- 

 liar nucleated cells; the fluid, however, is more abundant, and the cells are 

 fewer, than in the dentinal pulp. In the stratum of the pulp nearest to the 



1 In the above sketch of the history of the development of the Dentinal pulp, the account 

 given by Mr. Tomes has been followed, as that which the Author's own observations lead 

 him to prefer to the account given in former editions on the authority of Prof. Owen. See 

 also the "Beitriige BUT mikroskopischen Anatomic der menschlichen Ziihne," of Dr. J. 

 Czermak. 



