490 



OF NUTRITION. 



distinct prismatic cells, which formed (as it were) the moulds in which the 

 mineral substance was deposited.* According to Berzelius, the amount of 

 animal matter in the Enamel is less than 2 parts in 109 ; whilst the phosphate 

 of lime amounts to 885, the carbonate of lime to 8, and the phosphate of mag- 

 nesia to !. The Dentine} or Ivery consists of a firm substance, in which 



[Fig. 125. 



[Fig. 126. 



A view of the most interior portion of the main 

 tubes of the dental bone in an incisor of a child 

 two years old, close to their commencement in the 

 cavitas pulpi, in order to show their first division.] 



A view of the external portion of the tubes of 

 the same tooth, exhibiting their more minute rami- 

 fications, which, for the most part, turn towards 

 the crown.] 



mineral matter largely predominates, though to a less degree than in the ena- 

 mel. It is traversed by a vast number of very fine cylindrical branching wavy 

 tubuli, which commence at the pulp-cavity (on whose wall their openings may 

 be seen), and radiate towards the surface. In their course outwards, the tubuli 

 occasionally divide dichotomously ; and they frequently give off minute 



[Fig. 127. 



[Fig. 128. 



A view of a small portion of a transverse section of 

 the crown of the Tooth seen in fig. 120, viewed under 

 a magnifying power of 350 times ; 1, 2. 3, are the round 

 openings of the tubes, with parietes of a peculiar 

 substance ; 4, 5, 6, are the tubes cut more obliquely, 

 in consequence of their more external position.] 



A view of the position of the same main tubes, 

 in a transverse section near the root of a bicus- 

 pid, magnified 5 diameters. The dark patches 

 in this figure mark the places in which the bone 

 was especially white and less transparent than 

 in the clear intermediate tracts.] 



. * The Author has discovered a structure precisely resembling this, in the shells of 

 many Mollusca. See Annals of Natural History, December, 1843. 



j- A structure exactly resembling Dentine has been found by the Author in the shell of 

 the Crab, especially at the tips of the claws; and a less regular structure of the same 

 kind in the shells of many Mollusca (ioc. cit.). 



