1118 



SPLANCHNOLOGY 



I 



The Premolars or Bicuspid teeth (denies prcemolares) are eight in number, four 

 in each arch. They are situated lateral to and behind the canine teeth, and are 

 smaller and shorter than they. 



The crown is compressed antero-posteriorly, and surmounted by two pyramidal 

 eminences or cusps, a labial and a lingual, separated by a groove; hence their name 

 bicuspid. Of the two cusps the labial is the larger and more prominent. The 

 neck is oval. The root is generally single, compressed, and presents in front and 

 behind a deep groove, which indicates a tendency in the root to become double. 

 The apex is generally bifid. 



The upper premolars are larger, and present a greater tendency to the division 

 of their roots than the lower; this is especially the case in the first upper pre- 

 molar. 



The Molar Teeth (denies molares) are the largest of the permanent set, and their 

 broad crowns are adapted for grinding and pounding the food. They are twelve 

 in number; six in each arch, three being placed posterior to each of the second 

 premolars. 



The crown of each is nearly cubical in form, convex on its buccal and lingual 

 surfaces, flattened on its surfaces of contact; it is surmounted by four or five tuber- 

 cles, or cusps, separated from each other by a crucial depression; hence the molars 

 are sometimes termed multicuspids. The neck is distinct, large, and rounded. 



Upper Molars. As a rule the first is the largest, and the third the smallest of 

 the upper molars. The crown of the first has usually four tubercles; that of the 

 second, three or four; that of the third, three. Each upper molar has three roots, 

 and of these two are buccal and nearly parallel to one another; the third is lingual 

 and diverges from the others as it runs upward. The roots of the third molar 

 (dens serotinus or wisdom-tooth} are more or less fused together. 



Lower Molars. The lower molars are larger than the upper. On the crown 

 of the first there are usually five tubercles; on those of the second and third, four 



or five. Each lower molar has two roots, an 

 anterior, nearly vertical, and a posterior, 

 directed obliquely backward; both roots are 

 grooved longitudinally, indicating a tendency 

 to division. The two roots of the third molar 

 (dens serotinus or wisdom tooth] are more or 

 less united. 



The Deciduous Teeth (denies decidui; tem- 

 porary or milk teeth) (Fig. 1004). The decid- 

 uous are smaller than, but, generally speak- 

 ing, resemble in form, the teeth which bear 

 the same names in the permanent set. The 

 hinder of the two molars is the largest of all 

 the deciduous teeth, and is succeeded by the 

 second premolar. The first upper molar has only three cusps two labial, one 

 lingual; the second upper molar has four cusps. The first lower molar has four 

 cusps; the second lower molar has five. The roots of the deciduous molars are 

 smaller and more divergent than those of the permanent molars, but in other 

 respects bear a strong resemblance to them. 



Structure of the Teeth. On making a vertical section of a tooth (Fig. 1005), a cavity will be 

 found in the interior of the crown and the center of each root; it opens by a minute orifice at 

 the extremity of the latter. This is called the pulp cavity, and contains the dental pulp, a loose 

 connective tissue richly supplied with vessels and nerves, which enter the cavity through the 

 small aperture at the point of each root. Some of the cells of the pulp are arranged as a layer 

 on the wall of the pulp cavity; they are named the odontoblasts of Waldeyer, and during the 

 development of the tooth, are columnar in shape, but later on, after the dentin is fully formed, 

 they become flattened and resemble osteoblasts. Each has two fine processes, the outer one 



FIG. 1004. Deciduous teeth. Left side. 



