HUMAN DENTITION. 459 



prolonged to the extremity of the fang : a linear fissure is continued 

 from each angle of the base towards the corresponding angle of the 

 crown. The same cavity, exposed by a longitudinal section through 

 the thickness or antero-posterior cavity of the crown (ib. fig. 2), 

 is fusiform, its coronal end contracting to a linear fissure which is 

 continued towards the middle of the summit of the crown. The 

 pulp-cavity of the canine (ib. fig. 3), is relatively wider in its coronal 

 portion. In the upper premolars (ib. fig. 4), the coronal dilatation 

 sends a short and wide process to the base of each cusp, and is 

 continued from the opposite end in the form of two linear fissures, 

 one near the external, the other near the internal part of the com- 

 pressed apparently single fang. In the true molars (ib. fig. 7) a 

 short and wide process of the common coronal cavity is continued 

 towards the base of each tubercle of the grinding surface, and 

 as many linear prolongations as there are fangs, extend from the 

 opposite side of the cavity. In the broad fangs of the lower molars 

 the pulp-fissure commonly divides into two in each fang ; and in 

 the last or wisdom-tooth, which has frequently, at least in the 

 Caucasian races, a single implantation, the pulp-cavity always indi- 

 cates by its divisions the number of connate fangs that form such 

 undivided base. 



Every part of the surface of the pulp-cavity is pierced by 

 microscopic pores, about lojiouth of an inch in diameter, which are 

 orifices of tubes radiating from the pulp-cavity to the periphery 

 of the dentine with a general direction vertical to that surface ; 

 these are the dentinal or calcigerous tubes. In the lower incisor 

 and canine teeth, those from the middle of the summit of the pulp- 

 cavity ascend vertically to the enamel-covered surface of the 

 dentine at the summit of the crown ; the tubes on each side 

 of these gradually incline outwards ; those which go to the 

 angles of the crown forming an angle of 45° with the middle 

 vertical tubes : at the sides of the crown the tubes incline still more 

 outwards until in the middle of the fang they become horizontal, 

 and still lower, bend downwards. (1) The vertical tubes are nearly 



([) PL 122, fig. 1—3, d. 



