TISSUES OF THE BODY. 259 



cartilage (Koettiker), and another as a kind of fibro-cartilage (Reicliert). 

 The latter view is decidedly incorrect : we have before us most unmis 

 takably a young and undeveloped connective-tissue, with fusiform and 

 stellate cells. 



The diffuse calcification now advances superficially, as has just been 

 remarked, accompanied by a border of osteogenic tissue, so that the full 

 size and ultimate form of such, a secondary bone is only attained gradually, 

 in contradistinction to the cartilaginous preformations of the first kind. 



In order now that the bone may increase in thickness, a deposit of 

 osseous substance takes place from the periosteum on both surfaces, and 

 so the compact external layers are formed, which present at first all the 

 porous characters of newly-formed periosteal bony tissue. The deposit 

 of osteogenic matter from the medullary spaces resembles the process as it 

 occurs in bones previously modelled in cartilage. 



These observations tend to show what energy exists in the growth of 

 osseous tissue, an energy in which may be manifested afresh in fully 

 developed bone, especially under abnormal conditions. 



But though these processes, as we see them in the development of 

 cylindrical bones, are so far clear, we must not think that a solution 

 internally and a deposit externally alone takes place : there is some- 

 thing moro, namely, an interstitial and expansive growth ("a growth 

 by intussusception"), such as is to be observed in almost all tissues. 

 (R. Volkmann). 



But highly developed connective-tissue may also, under certain circum- 

 stances, be transformed directly into bony substance. The flat cranial bones 

 of embryonic birds (fig. 249) present to us most unmistakably, according 

 to Gegenbaur, a process of this kind. Here a network of connective-tissue 

 bundles is seen (c), in part still soft and fibrillated and in part granularly 

 calcified (d). Later on these bands of hardened tissue become broader, 

 are now diffusely calcified, while the cells enclosed in them remind one 

 of bone-corpuscles. A layer of osteoblasts (&, e) is also demonstrable here, 

 which deposits that stratum of bone clothing the connective-tissue frame- 

 work. That we have to do here with an occurrence which, taken gene- 

 rally, has been already discussed in referring to the formation of Sharpens 

 fibres, is quite apparent. 



The conversion of tendons into osseous tissue is well known to take 

 place largely as a physiological occurrence in mature birds. Here we 

 encounter, at first, a simple calcification of the connective-tissue, so that, 

 on depriving the part of its bony earth, the tendinous texture is again 

 presented to us unchanged. Later on, however, true osseous substance 

 makes its appearance, with a small number of lacunae, lamellae, and 

 Haversian canals. It was formerly supposed that here a direct transfor- 

 mation took place from tendinous into osseous tissue (Lieberlculm), but 

 this is an error. There appear, rather, in the calcified tendon, spaces 

 containing vessels which correspond to the medullary sinuses of cartilage, 

 and are filled with a soft mass. From these cavities the deposit of a solid 

 substance takes place, which becomes calcified at once, " resembling true 

 bone more or less" (H.Muller). Eemnants of calcified connective-tissue 

 are left, however, in these ossified tendons. 



Regeneration of osseous tissue occurs pathologically, with great fre- 

 quency, on the fracture of various bones, for the repair of breaches of 

 continuity and replacement of lost substance, whether it have been 

 thrown off by a pathological process or removed by surgical instruments ; 



