DEVELOPMENT OF BONE. 139 



as appears from its examination with high powers, of decus- 

 sating fasciculi of connective tissue divided in various direc- 

 tions in the section. Between the fibrillse fusiform cells with 

 elongated nuclei are distributed. To this external layer of the 

 periosteum succeeds a tolerably broad internal layer b (Cam- 

 bium),* which with low powers is distinguished by its containing 

 a large number of small round bodies that appear to be imbedded 

 in the meshes of a fine plexus, and confer upon it a granular 

 aspect. If we examine these layers separated from one 

 another under high powers, and combine therewith the results 

 obtained from the investigation of preparations teased and pen- 

 cilled out, we shall observe in the first place that the granu- 

 lar appearance depends upon the presence of small roundish 

 nucleated cells. The cells give off a variable number of fine 

 processes from their periphery, which join the reticulum ; the 

 latter possesses a structure which it is difficult to unravel, for 

 we do not find in it the well-developed stellate cells present 

 in the reticulum of the lymphatic glands, but flattened cells 

 that are finely granular in the portion lying next to the nucleus, 

 and at various points, but frequently only at the two opposite 

 poles, give off long homogeneous processes. In very many 

 instances the isolated cells become continuous at their peri- 

 phery with a fine trabecular trellis-work of wing-like form 

 connected with other fine and smooth trabeculse traversing 

 the reticulum. 



On the internal surface of the second layer of the periosteum 

 which we have just described, there follows a third layer c, 

 which contains large granular cells exactly comparable to the 

 above-mentioned osteoblasts, and forms an epithelial covering 

 continuous with the periosteal investment of the bony trabe- 

 culse. By teasing out the specimen with needles, it may be 

 demonstrated that the apparently spherical cells are here also 

 provided with numerous fine homogeneous processes, which on 

 the one hand penetrate into the already described reticulum, 

 or on the other hand extend to the surface of the bone, into 

 the substance of which they pass without interruption. 



The cellular investment of the osseous trabeculse is, however, 



* Billroth, Archivfur klinische Chirurgie, Band vi., p. 723. 



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