J S4 



TEXT-BOOK OF PHYSIOLOGY. 



irregular stellate spaces, the interglobular spaces, between the dentine 

 and the cementum, which are occupied by connective-tissue cells. 

 Clefts of varying size are also observed at the junction of the dentine 

 and the enamel, and which extend for some distance into the latter. 

 The enamel is composed of dense hard cylinders which, on account 

 of their small size and close relationship, appear to be hexagonal in 

 shape. These cylinders are held together by cement substance. The 

 free border of -the enamel is covered, in early life at least, by a thin 



membrane known as the cuticle or 

 membrane of Nasmyth. 



The dentine is somewhat less dense 

 than the enamel. It is composed of 

 connective-tissue fibers embedded in 

 a ground- substance, both of which 

 have undergone calcification in the 

 course of development. The dentine 

 is penetrated by a series of fine canals, 

 the dentine canals or tubules, which 

 begin by open mouths on the pulp 

 side. From this point the tubules 

 pass outward to the cementum and 

 enamel, where their terminal branches 

 communicate with and terminate in 

 the interglobular spaces and clefts. 

 In their course the tubules give off a 

 series of branches which communicate 

 freely with one another. The dentine 

 bordering the tubule is somewhat 

 more dense than the intertubular por- 

 tion and constitutes what is known 

 as the dentinal sheath or Neumann's 

 sheath. 



The cementum resembles bone be- 

 cause it contains both lacunae and 

 canaliculi, though it is, as a rule, 

 devoioTof Haversian canals. 



The pulp consists of a framework of connective tissue which 

 affords support to blood-vessels and nerves, both of which enter the 

 pulp chamber through a small foramen at the apex of the root. The 

 outer surface of the pulp is covered with a layer of large spheric 

 cells, the odontoblasts. Each cell presents on its inner surface short 

 processes which pass into the pulp ; on its outer surface it presents a 

 long process which enters a dentine tubule and extends as far as its 

 ultimate terminations. Collectively these processes are known as 

 the dentine fibers. Inasmuch as the fibers do not completely occupy 



RM. 



C 



FIG. 60. VERTICAL SECTION OF 

 TOOTH IN JAW. E. Enamel. 

 D. Dentine. P. M. Periodontal 

 membrane. P. C. Pulp cavity. 

 C. Cement. B. Bone of lower 

 jaw. V. Vein. a. Artery. N. 

 Nerve. 



