290 MICROSCOPIC ANATOMY OF THE TEETH 



cular system of the bony tissue' (7). These remarks will 

 apply with equal force to cement. 



It is claimed by Walkhoff and by Hope well Smith (4) that 

 normal cement does not contain lacunae, but while these 

 are rarely found in the thin layer at and near the neck of 

 the tooth, there seems little doubt they are abundantly 

 present in that of the root, and in the development of the 

 cement at the growing root tip they are distinctly seen 

 becoming included in the forming tissue. It would appear 

 that if all cement containing lacunae is to be looked upon 

 as pathological, there would be very few teeth that could 

 be said to possess normal cement. In fig. 190 lacunae are 

 seen in the thin layer on the outside of the root where 



FIG. 183. Bone cell isolated (Schafer after Joseph), a. Proper wall of 

 lacuna shown at a part where the corpuscle has shrunk away from it ; 

 c. cell ; n. nucleus. 



the deposition of this tissue has apparently been quite 

 normal. 



The cement at the neck of the tooth is clear and 

 translucent, and seldom shows any trace of lamination ; but 

 in the root portion of the tissue the lamellae are very con- 

 spicuous, and represent lines of incremental growth as in bone. 



The processes of the lacunal cells communicate with one 

 another and with the fine terminations of the dentinal tubes 

 in the granular layer of the dentine. They thus, where 

 present, form a chain of communication of protoplasmic 

 material between the periodontal membrane and the pulp, as 

 is clearly shown in figs. 184-186 from a tooth of a marsupial, 

 and in a human molar in fig. 187. Those who deny the 

 existence of lacunae in normal cement would not admit 

 that such intercommunication exists. 



As in bone, the perforating fibres of Sharpey are seen to 



