THE MOUTH 413 



or succedaneous set. The former are 20 in number, 10 in each 

 jaw; the latter, 32, 10 each above and below. Each tooth is 

 made up of three parts: the root, consisting of one or more 

 fangs, contained in the alveolus; the crown, or body, above 

 the gum; and the neck, between the two. The alveolar peri- 

 osteum is reflected on to the fang as far as the neck. 



The twenty temporary teeth are divided into 4 incisors, 2 

 canines, and 4 molars above and below. The 32 permanent 

 teeth are, 4 incisors, 2 canines, 4 bicuspids, and 6 molars in 

 each jaw. The temporary teeth are similar to but smaller 

 than the permanent; of the temporary molars, the hinder one 

 is the largest of all, and its place is afterward taken by the 

 second permanent bicuspid. 



Of the permanent teeth the incisors are the 8 central cutting 

 teeth, 4 each above and below, the former being the larger. 

 They are bevelled at the expense of the posterior surface. 

 The canines (cuspidati} are 2 in each jaw, being situated 1 

 behind each lateral incisor, the upper and larger being called 

 the eye teeth. The bicuspids (prcmolars or false molars}, 

 4 in each jaw, lie 2 each behind the canines, the upper being 

 the larger. The molars (true- molars or multicuspidati) are 

 the largest teeth, and number 6 in each jaw, 3 each behind the 

 posterior bicuspids above and below. They present 4 tubercles 

 on the upper, 5 on the lower crowns, and the root is subdivided 

 into from 2 to 5 fangs. The first molar is the largest and 

 broadest, the second smaller, and the third (wisdom tooth) 

 the smallest. 



A vertical section of a tooth shows it to be hollow, the cavity 

 being continuous with the* aperture in the fang and filled up 

 with the soft dental pulp, and is hence called the pulp cavity. 

 The pulp is sensitive, highly vascular, and consists of con- 

 nective tissue, with cells, vessels, and nerves. The hard 

 substance of each tooth consists of three parts: the ivory t 

 or dentine, the enamel, and the crusta petrosa, or cement. 



Eruption. The teeth are erupted by the absorption of the 

 bone between them and the gum, as well as that covering the 

 labial side of the crown. Thus they are not an upward growth 

 of the tooth, but appear as a result of the absorption of the 

 bone around the crown. The bone covering the lingual surface 

 is more slowly absorbed, as it protects the permanent tooth 

 germ beneath. 



