108 DEVELOPMENT OF THE TEETH. 



gradually increases, and the pulp diminishes within it. The 

 body of the tooth is produced first, and the root is formed 

 gradually afterwards ; during its formation the root has a large 

 opening at the extremity, which is gradually diminished to the 

 small orifice before described. The roots, as well as the body, 

 are formed upon the pulpy substance, which gradually 

 diminishes, as they increase. After the external surface of the 

 body of the tooth is formed* the enamel begins to appear 

 upon it, and gradually increases, until it is completely invested. 

 It is probable that the enamel is deposited upon the body of 

 the tooth by the membranous capsule which contains it. This 

 substance, which appears to be formed of radiated fibres, is 

 harder and less destructible than bone. Like the substance 

 of bone, it is composed of phosphate, with a small propor- 

 tion of the carbonate of lime; but it is destitute of the cartila- 

 ginous or membraneous structure which is demonstrable in 

 bone. 



The pulpy substances, or rudiments of teeth, may be seen in 

 the foetus, when about four months old. At six months, 

 ossification can be seen to have commenced on the pulps of 

 the incisores. At the time of birth, the bodies of the infant 

 teeth are distinctly formed. The alveoli, at first, have the 

 appearance of grooves in the jaw, which afterwards are divided 

 by transverse partitions ; they enlarge, in conformity to the 

 growth of the teeth, and appear to be altogether influenced by 

 them. 



The permanent teeth are formed very early : the rudiments 

 of the first permanent grinder on each side have commenced 

 their ossification at birth. At the same time, the rudiments of 

 the permanent incisors are to be perceived ; and their bodies 

 will be found nearly ossified, by the time the infant incisors 

 are protruded completely through the gums. About the age of 

 six years, if none of the infant teeth are shed, there will be 

 forty-eight teeth in the two jaws, viz : the twenty infantile, 

 and twenty-eight permanent teeth, more or less completely 

 formed. 



From their mode of development, apparent structure, and 



.c *&f* 



