DEVELOPMENT OF THE TEETH. 489 



and we soon recognise a solid shell of dentinal bone superim- 

 posed on the dentine germ, like a cap. The histological forma- 

 tion of the dentine is precisely similar to the ordinary process 

 of ossification. 



Whilst the peripheric portions of the odontoblasts constantly 

 undergo metamorphosis, with disappearance of their nuclei, 

 into a gelatigenous matrix which subsequently undergoes 

 calcification, their centric portions penetrate the hardened mass 

 in the form of longer or shorter threads, and represent the first 

 rudiments of the dental fibres. The lateral processes of the 

 odontoblasts occasion the numerous anastomoses of the dental 

 fibres, or of the dental tubuli. Every odontoblast communi- 

 cates with the more deeply situated and successively enlarging 

 cells of the young pulp by means of its pulp process, so that 

 when an odontoblast is calcified up to the base of the fibre, 

 another occurs in its place without any interruption to the 

 continuity of the fibre. Hence every dental fibre, with its 

 anastomoses, must be regarded as formed of several continuous 

 odontoblasts. The layers of matrix immediately surrounding 

 the fibres undergo conversion, as appears from their chemical 

 characters, into elastic tissue, and form the dental sheaths of 

 Neumann. It has not yet been ascertained whether they 

 also undergo calcification. Thus it appears that the dentine, 

 with all its constituents, proceeds from odontoblasts that have 

 become metamorphosed in their form and chemical com- 

 position. 



No further detail respecting the process of dentinification need here 

 be entered upon, since, so far as regards the osteoblasts, it presents 

 the most complete analogy to that of ossification (see p. 135). 



This analogy is still more close in regard to the formation of 

 the cement, in which the histological processes are identical 

 with those of intra-membranous ossification. The matrix of 

 the cement is the loose myxomatous connective tissue of the 

 dental alveoli which immediately surrounds the teeth, and so 

 far we may thus consider the dental sacculus to be the matrix 

 of the cement. A special cement germ, such as has been 

 described by Kobin and Magitot (46), in certain species of 



