260 



MANUAL OF HISTOLOGY. 



further, in uninjured bones a luxuriant growth may occur, in the form of 

 hypertrophies, exostosis, and osseous tumours. In most of these cases 



the production 01 the new tissue 

 takes place from the periosteum 

 in the manner described. "With- 

 out this, however, we may be 

 satisfied of the great importance 

 of the membrane in the produc- 

 tion of bone from Oilier 's experi- 

 ments (p. 257). But while the me- 

 dullary tissue remains inactive 

 in the normal formation of bone, 

 as was ascertained by the inves- 

 tigator just mentioned, it may, 

 under abnormal conditions, be- 

 come transformed into a more 

 or less solid connective -tissue 

 on its exterior into a species of 

 endosteum, and generate bone- 

 like matter. The latter is rarely 

 developed in soft parts remote 

 from bone. The formation of 

 true osseous tissue independent 

 of bone is very circumscribed. It 

 takes place, however, far on in 

 life in cartilage, and at its ex- 

 pense, when the processes of 

 foetal ossification are repeated ; 

 likewise in parts formed of con- 

 nective-tissue, when a growth 

 similar to that from periosteal 

 osteogenic substance is the start- 

 ing-point. Masses of bone formed pathologically have frequently a porous 

 character at first, resembling the normal tissue, but may also be com- 

 pact, and endowed with a high degree of solidity. 



The occurrence of re-solution of normal osseous tissue is by no means 

 rare in disease. It takes place with previous decalcification, in the same 

 way as physiological absorption in growing bone. 



REMARKS. From the fact that bones not previously modelled in cartilage are in 

 many cases developed before those others become ossified which are thus pre-formed, 

 \ve may perceive that the designation "secondary" has not been very happily 

 applied" to them. An attempt has been made, therefore, to replace ic by the names 

 " tegumentary or overlaying bone" (Deck-or Belegeknochen). The whole thing has 

 lost considerably in histological worth, however, according to the latest observations 

 in osteogenesis. 



11. Dentine. 

 150. 



Before entering upon the description of dentine (1), it will be necessary 

 first to devote a few words to the consideration of the teeth, the greater 

 part of which it forms. 



A tooth may be divided into three distinct parts, into the crown, 

 which lies exposed ; the neck, enclosed in the gum ; and the root, buried 



Fig. 249. From the edge of the frontal bone of a 

 chick undergoing ossification (from Gegenbaur). a, 

 network of osseous bands ; d, granularly calcified, 

 and c, soft connective-tissue ; 6, e, osteoblasts. 



