DENTINE 253 



The odontoblasts in old age atrophy and disappear, and 

 sometimes the whole pulp is occupied by dense connective 

 tissue in which no cells, blood-vessels, or nerves are to 

 be seen. The pulp may also undergo fatty degeneration. 



Vascular canals are occasionally seen in human dentine, 

 especially in the root portion of the tooth. 



Plicidentine. The ultimate structure of plicidentine is 

 similar to that of ordinary orthodentine, but the pulp 

 chamber, instead of being of a simple form and occupying the 



FIG. 155. Transverse section of plicidentine tooth of Zygobatis, 

 showing intercommunicating tubes of the columns radiating from the 

 pulp cavities. (250.) 



centre of the tooth, is folded upon itself, each portion of 

 the pulp having its separate system of radiating tubes, the 

 intricate foldings so produced forming a very complicated 

 pattern in many of these teeth (fig. 155). There may be a 

 central pulp cavity which sends out offshoots to the different 

 portions of the folded dentine, forming a star-shaped figure 

 as seen in Lepidosteus, or as in Lepidosteus spatula there 

 may be no definite central pulp cavity but the position 

 of this central portion is occupied by numerous small 

 radiating systems of tubes around small ingrowths of the 

 pulp. Around this central system are long processes of 



