THE TEETH 253 



glandular epithelial cells of the secreting portions become swollen 

 and clear after a period of rest, but are shrunken and present a 

 faint cytoplasmic reticulum after activity. The different glands 

 of the same region, and even different cells in the same gland, 

 often exhibit various stages of secretory activity. The fundus 

 of the secreting glands frequently extends into the loose con- 

 nective tissue of the submucosa. At the margin of the lips and 

 more rarely in the neighboring portions of the buccal mucous 

 membrane are small sebaceous glands which open directly upon 

 the free surface. 



THE TEETH 



Each tooth rests in a bony socket in the alveolar process of 

 the maxillary bone, and is also held in place by the periosteum 

 of the alveolar sac and the adjacent portion of the gum. The 

 tooth is divisible into a free portion or crown, and a concealed 

 portion or root which usually consists of one to three fangs. The 

 slightly constricted border between the root and the crown, which 

 is surrounded by the soft tissues of the gum, is known as the neck 

 of the tooth. 



The tooth also contains a superficial calcareous portion and a 

 central medulla, the pulp cavity, which occupies the axis of the 

 tooth and which contains a peculiar embryonic type of connective 

 tissue, the dental pulp. At the tip of each fang a narrow canal 

 penetrates the wall of the tooth and permits the entrance of the 

 nerves and blood vessels which supply the pulp cavity. 



The calcareous wall of the tooth is formed by three distinct 

 tissues : 1, dentine ; 2, enamel ; 3, cementum. The dentine incloses 

 the entire pulp cavity and is in turn covered by the enamel and 

 cementum, the enamel forming the superficial layer of the crown, 

 the cementum that of the root of the tooth. 



The dental pulp is an embryonic type of connective tissue which 

 is rich in branching stellate cells and poor in fibres. It contains 

 no elastic fibrils, and the delicate white fibres instead of forming 

 bundles are arranged in an interlacing network, the fine fibrils of 

 which are in intimate relation with the connective tissue cells. 

 The stellate connective tissue cells are scattered throughout the 

 entire pulp, but at the periphery of the cavity are closely crowded 

 and are much enlarged. These peripheral cells form a layer of 

 odontoblasts which is in contact with the dentine. 



The odontoblasts are cylindrical branched connective tissue 

 cells whose long axis is perpendicular to the surface of the adja- 



