188 ANTHROPOLOGY. 



divisions in the upper and two in the lower. These last teeth, however, 

 are very variable as to size and other characters, and occasionlly are not 

 protruded, particularly in the upper jaw. 



Every tooth, when divided, presents an external shell or cortex, and an 

 internal cavity which extends beneath the crown, partly corresponding to it 

 in form, and contracts as it descends through the root into a fine tube, which 

 ends in a minute foramen. In the young and growing tooth this cavity is 

 large, and contains a soft, vascular pulp or bulb ; in the course of time it is 

 much diminished by surrounding osseous or ivory deposit, and in the adult 

 or aged contains little more than a vascular lining membrane. The walls 

 of this cavity, though very firm, are perforated by numerous minute pores, 

 which lead into the solid texture of the tooth. The substance of a tooth 

 consists of three elements : enamel, ivor}- or dentine, and crusta petrosa or 

 cement. The enamel covers the crown ; the ivory forms the greater por- 

 tion of the body and root; and the crusta, in the form of a thin lamina, 

 invests the root only, though, according to some, it is also prolonged over 

 the crown and enamel. 



The teeth make their appearance at a very early age of the foetus, 

 although requiring a long time for their full development ; it is not till the 

 sixth or seventh month after birth that the two middle incisors of the lower 

 jaw come out. The remaining incisors follow at intervals of from four to 

 six weeks ; first the two median upper ones ; then the two exterior lower, 

 and lastly the two exterior upper. The uppt ..^d lower anterior molars of 

 each side of the jaw next make their appearance, followed by the canines, 

 and finally by the posterior molars. At the end of the second year the 

 child has twenty teeth. These are called milk teeth, from making their 

 appearance during the period of suckling. The incisive and canine milk 

 teeth are smaller than the permanent ; the posterior molars on the other 

 hand are larger. About the seventh year the milk teeth fall out and are 

 replaced by the permanent, in nearly the same order as that of their first 

 appearance. After all the incisors are changed, the anterior and posterior 

 temporary molars are successively shed, and replaced by the permanent 

 bicuspids ; the canines are not changed before the tenth or eleventh year. 

 After the twelfl^h or thirteenth the second permanent molars appear, and the 

 last or dentes sapientiee (wisdom teeth) seldom before eighteen or twenty, 

 and occasionally at a much later period. 



PI. 123, fig. 18, the teeth of both jaws from before. Fig. 19, do. from 

 the side. Fig. 20, the lower jaw of a child four years old with the milk 

 teeth and their sockets. Fig. 21, the same for the upper jaw. Figs. 22 

 and 23, upper and lower jaw opened, with the milk and permanent teeth in 

 their sockets or alveoli. Fig. 24, dental sac of a milk tooth with its vessels. 

 Fig. 25, do. of a permanent tooth. Fig. 26, vertical section of the tooth 

 cavity contained by the sac. Fig. 27 «-e, the teeth of the right upper jaw 

 of a fcetus of about eight months. Fig. 28 a-e^ teeth of a newborn child. 

 Fig. 29 a-e, teeth of a child of four years. Fig. 30, second set of upper 

 jaw teeth of a four years' old child seen from within. Fig. 31, do. from 

 below. Fig. 32, teeth of a child at seven years : A, milk teeth ; B, per- 

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