108 A MANUAL OF DENTAL ANATOMY. 



entirely converted into secondary dentine, but it would seem 

 to be very generally the case that those teeth which exercise 

 very active functions and last throughout the life of the 

 creature retain their pulp in an active and vascular condition. 



THE GUM. 



The gum is continuous with the mucous membrane of 

 the inside of the lips, of the floor of the mouth, and of the 

 palate, and differs from it principally by its greater density. 

 Its hardness is in part due to the abundant tendinous fasci- 

 culi which it itself contains, in part to its being closely 

 bound down to the bone by the blending of the dense fibrous, 

 fasciculi of the periosteum with its own. The fasciculi 

 springing from the periosteum spread out in fan-like shape 

 as they approach the epithelial surface. There is thus no 

 very sharp line of demarcation between the gum and the 

 periosteum when these are seen in section in situ. 



The gum is beset with rather large, broad-based papillae, 

 which are sometimes single, sometimes compound; the 

 epithelium is composed of laminee of tesselated cells, much 

 flattened near to the surface ; but cylindrical cells form the 

 deepest layer of the epithelium, the rete malpighi. 



Small round aggregations of pavement epithelium are 

 met with at a little depth, or even bedded in the surface ; 

 these, the "glands" of Serres, have no known significance. 

 In the neighbourhood of developing tooth-sacs epithelial 

 aggregations of similar appearance are to be met with, and 

 in such spots are remains of the neck of the enamel organ 

 (cf. page 137), which has undergone this curious change 

 subsequently to the completion of its original function. 

 The gums are rich in vessels, but remarkably scantily sup- 

 plied with nerves. 



