156 



MICROSCOPIC ANATOMY OF THE ORGANS. 



similar to that of the blood-vessels. The sensory nerves end 

 in the mucous membrane in two ways : on the papillae as 

 Krause's end bulbs, and in the epithelium as fine intra-epithelial 

 nerve-endings (see under Nerve-endings). 



2. The Teeth. 



The teeth in man and the higher animals are hard struct- 

 ures, of which one part is sunk in the alveolus of the jaw 

 (root] and the other part projects to the outside, and is called 

 the crown of the tooth. The place of junction of the two parts 

 is called the neck of the tooth, and this part is covered by the 

 gum. 



The teeth consist of three hard substances: 1, enamel; 2, 

 dentine; 3, cement. These substances surround a cavity in 



FIG. 111. 



Odontoblasts 



Dentine 



Connective & 



tissue cells' 



'\^L^Jt& 



From a longitudinal section of the crown of a milk tooth of a newborn haby. The 

 boundary between pulp and dentine is shown. X 500. 



the centre of the tooth known as the pulp- or tooth-cavity. 

 This cavity extends into the root of the tooth as the root- 

 canal, through which vessels and nerves enter the pulp from 

 below. 



The tooth pulp consists of a finely fibrous cellular con- 

 nective tissue, and is characterized by its richness in nerves and 

 blood-vessels. On the surface of the pulp there are large cells 



