74 THE CONNECTIVE TISSUES. [CH. V. 



cavity is called the pulp cavity from its containing the very 

 vascular and sensitive pulp. 



The tooth-pulp is composed of loose connective tissue, blood- 

 vessels, nerves, and large numbers of cells of varying shapes, e.g., 

 fusiform, stellate, and on the surface in close connection with the 

 dentine a specialised layer of cells called odontoblasts, which are 

 elongated columnar-looking cells with a large nucleus at the 

 tapering ends farthest from the dentine. 



The blood-vessels and nerves enter the pulp through a small 

 opening at the apical extremity of each root. The exact termina 

 tions of the nerves are not definitely known. They have never 



Fig. 95. Section of a portion of the dentine and cement from the middle of the root of an 

 incisor tooth, a, dentinal tubules ramifying and terminating, some of them in the inter- 

 globular spaces ft and c; d, inner layer of the cement with numerous closely set 

 canaliculi ; , outer layer of cement ; /, lacunae ; g, canaliculi. x 350. (Kolliker.) 



been observed to enter the dentinal tubes. No lymphatics have 

 been seen in the pulp. 



A layer of very hard calcareous matter, the enamel, caps that 

 part of the dentine which projects beyond the level of the gum ; 

 while sheathing the portion of dentine which is beneath the level 

 of the gum, is a layer of true bone, called the cement or crusta 

 petrosa. 



At the neck of the tooth, where the enamel and cement come 

 into contact, each is reduced to an exceedingly thin layer ; here 

 the cement overlaps the enamel and is prolonged over it. On 

 the surface of the crown of the tooth, when it first comes through 

 the jaw, is a thin membrane called Nasmyth's membrane, or the 

 cuticle of the tooth. The covering of enamel becomes thicker 

 towards the crown, and the cement towards the lower end or apex 

 of the root. 



Dentine or Ivory. 



Chemical composition. Dentine closely resembles bone in 

 chemical composition. It contains, however, rather less animal 



