THE TEETH. 



645 



They are covered by smooth and vascular mucous membrane, which is remarkable 

 for its limited sensibility. Around the necks of the teeth, this membrane 

 presents numerous fine papillae; and from this point it is reflected into the 

 alveolus, where it is continuous with the periosteal membrane lining that 

 cavity. 



THE TEETH. 



The human subject is provided with two sets of teeth, which make their ap- 

 pearance at different periods of life. The first set appear in childhood, and are 

 called the temporary, deciduous, or milk teeth. The second set, which also appear 

 at an early period, continue until old age, and are named permanent. 



The temporary teeth are twenty in number ; four incisors, two canine, and four 

 molars, in each jaw. 



The permanent teeth are thirty- two in number ; four incisors (two central and 

 two lateral), two canine, four bicuspids, and six molars, in each jaw. 



General characters. Each tooth consists of three portions ; the crown or body, 



Fig. 320. The Permanent Teeth. External View. 



Molurt 



Jciur 



Bicuspid* Canine Jncirort 



JLower Jawr 



Alolurl 



which projects above the gum ; the root or fang, entirely concealed within the 

 alveolus ; and the neck, the constricted portion between the other two. 



The roots of the teeth are firmly implanted within the alveoli : these depressions 

 are lined with periosteum, which is reflected on to the tooth at the point of the 

 fang, and covers it as far as the neck. At the margin of the alveolus, the peri- 

 osteum becomes continuous with the fibrous structure of the gums. 



