140 THE CONNECTIVE TISSUES, BY A. ROLLETT. 



not continuous, since between the separate granular osteoblasts 

 the somewhat expanded processes of the before-mentioned 

 reticulum penetrate and proceed directly to the surface of the 

 bone, into the matrix of which they pass without apparent 

 interruption. In correspondence with the larger size of the 

 osteoblasts, the meshes of the reticulum of bone are likewise 

 enlarged. 



Such are the appearances presented by a transverse section 

 in which fully formed bone, layers of osteoblasts, and small- 

 celled and fibrillar periosteal layers immediately succeed one 

 another in parallel series. 



This, however, can be observed only in a few places. 

 The external form of the transverse section shown in fig. 15 is 

 conformed to the shape of the external and internal limits of 

 the fibrillar portions of the periosteum. The internal surface 

 of the bone everywhere invested with osteoblasts is, on the 

 other hand, irregularly bulged and dentated, whilst the arcuate 

 boundaries of the cavities occurring in the bone project towards 

 the periosteum. From the arches of the completely developed 

 bone other arches spring, which, exclusively composed of 

 osteoblasts, are directly continuous with the osteoblasts in- 

 vesting the bony trabeculse. The last-named arches are either 

 entirely closed externally, forming completely differentiated 

 rings of osteoblasts, or we may observe two arched processes 

 inclined to one another, constituting the commencement of a 

 future ring. These incomplete arches then enclose a part of 

 the already described small-celled second layer of the perios- 

 teum, the enclosed and the unenclosed portions being continuous 

 through the orifice left in the crown of the arch, and in the 

 first instance presenting identical characters. We have thus 

 acquired a knowledge of the first formation of the Haversian 

 system and canals, as well as of the medulla primarily con- 

 tained in the latter. In passing from without inwards we may 

 recognise all stages of transition from the first formation of the 

 projecting osteoblastic arches, and from the first incomplete 

 arches projecting from the bone, and closed only by an osteo- 

 blastic layer, to the completely closed lamellae of bone. All 

 these newly formed rings and arches of bone are invested on 

 their inner surface with osteoblasts, and upon their external 



