136 THE CONNECTIVE TISSUES, BY A. ROLLETT. 



Gegenbaur supposes the osteoblasts to form a hardening secre- 

 tion, in which they are subsequently themselves enclosed, 

 appearing in the form of the stellate bone corpuscles. Wal- 

 deyer has drawn attention to the difficulties of this explanation, 

 and has sought to show that the osteoblasts are constantly 

 converted into bone in a lamellar fashion, whilst new layers 

 are constantly being differentiated from the medulla. In 

 undergoing this change the osteoblasts assume a smoother and 

 more homogeneous appearance, and, whilst their nuclei break 

 down and vanish, become hardened into the matrix of bone 

 in some of them, however, only the external portions undergo 

 this fusion and calcification, the inner portion with the nucleus 

 remaining as bone cells enclosed in a stellate cavity. The 

 latter explanation corresponds with much greater exactness 

 than the former to the facts that have been observed. 



Before discussing this subject further, we shall now proceed 

 to show that the formation of bone in periosteal tissue and in 

 investing bones occurs under the same conditions as those of 

 which we have acquired a knowledge when considering intra- 

 cartilaginous ossification. In reference to the latter it must still 

 be remarked that although the exposition given above has been 

 especially derived from the examination of human embryoes, 

 it has also been observed in allied animals. 



In describing the processes taking place at the ossifying 

 surface of the diaphyses, we have already become acquainted 

 with those which determine the increase in length of the 

 tubular bones. Their increase in thickness is dependent upon 

 the processes we are now about to describe. Grew* and 

 Haversf were the first to point out that a deposit of new bone 

 takes place upon that already formed from the periosteum, 

 but it was the researches of Du HamelJ that led to the general 

 recognition of the fact. 



In the development of the tubular bones, the process of 

 periosteal ossification may even precede the intra-cartilagmous. 



* English Academy, 1681. 



t Osteologia, etc. Frankfurt and Leipzig, 1692. 



J Memoir -es de V Academic de Paris, 1742, p. 354 ; 1743, pp. 87, 111, and 



288. 



