DEVELOPING TOOTH. 45 



Tomes fibres pass into the tubules. They are better seen in 

 the developing tooth. Find tubules cut transversely and note 

 the appearance of a tubular wall. 



Young tooth. Early stage. T.8. Fore part of head of 

 embryonic rat. (p. 14 (b), s. 22 & 24, c. P., m. B.) (L) Find the 

 cavity of the mouth, and the epithelium with stained nuclei 

 which lines its surface. Note in each jaw, on each side, the 

 dental groove filled with epithelium, from which flask-shaped 

 prolongations project inwards, the future enamel organs. Each 

 of these has a conical recess on its inner aspect which 

 accommodates the dental papilla. The latter at this stage 

 shows only as a collection of nucleated cells. 



Young tooth. Later stage. V.T.S. Jaw of kitten, (p. 14 (/>), 

 s. 22 & 24, c. P., m. B.) (L) The enamel organ developed from 

 the flask-shaped mass of cells, is larger and exhibits epithelium 

 on its surface only, the interior of the organ being occupied by 

 delicate branching tissue. The surface cells are squamous in 

 single layer, excepting over the conical recess, which fits upon 

 the papilla ; here there are several layers, the most superficial 

 of which is columnar. These columnar cells produce the enamel 

 prisms. The enamel forms a thin layer, thickest at the apex 

 of the cone and tapering towards the edges. It consists of 

 enamel prisms set side by side. Where these are detached 

 from the columnar cells processes from the latter should be 

 sought for, which have been wrenched out of the enamel prisms, 

 in which they were embedded. 



In immediate contact with the enamel is a layer of dentine, 

 forming a conical cap to the papilla, the tissue of the papilla 

 or pulp of the tooth consists of a prominent layer of odonto- 

 blasts next to the dentine from which a narrow space often 

 appears to separate them owing to removal of uncalcified matrix 

 by the reagent and across which the Jibres of Tornr* run from 



