OSSEOUS TISSUE. 



855 



Fig. 458. 



temporary cartilage on the approach of ossifi- 

 cation is that the corpuscles, instead of being 

 solitary, are arranged in groups of variable 

 numbers according as they are near or far off the 

 site of immediate ossification ; that they have 

 a linear arrangement, and where there are two 

 or three only this is somewhat semilunar, with 

 the straight edges near each other ; and that the 

 greatest diameter is lateral. (See jig. 457, b.) 

 Moreover, the columns are not continued unin- 

 terruptedly through the cartilage, but are broken 

 off, and near their terminations new ones com- 

 mence, not, however, in a line with the former, 

 but opposite their intercolumnar spaces. (See 

 fg- 458.) 



Supposing this view of 

 the subject to be correct, as 

 I believe it to be, the growth 

 of a bone in its length ad- 

 mits of easy solution, name- 

 ly, by the developement of 

 cartilage at the epiphyses. 

 The formation of co- 

 lumns having commenced, 

 developement in the lines 

 proceeds with rapidity, and 

 the corpuscles composing 

 them hold a different rela- 

 tion to each other at each 

 part of the same column. 

 Thus atthe end farthest from 

 the point of ossification the 

 corpuscles are flattened and 

 closely arranged, present- 

 ing an appearance not un- 

 like a pile of pence. But as 

 we trace the line down to- 

 wards the bone, each corpuscle becomes more 

 distinct, is separated from those on either side, 

 becomes itself enlarged, and of nearly equal 

 dimension in each direction. (See figs. 458 and 

 460.) The intercellular tissue becomes distinctly 

 visible between each corpuscle. The space also 

 between the columns, though always consider- 

 able, is increased when the corpuscles have 

 undergone the above change. (See fig. 459.) 



Fig. 459. 



Temporary cartilage, 

 with corpuscle arran- 

 ged in columns. 



a, intercolnmnar 

 or cellular tissue j b, 

 parietes of the cor- 

 puscle ; c, central 

 cavity of the corpus- 

 cle. 



Fig. 460. 



and relative position observable, but a further 

 remarkable developement takes place in each 

 corpuscle. The parietes of the cell, which at 

 first formed but a small part of the whole, at 

 this latter situation has so far increased in di- 

 mension that it forms by far the greater part of 

 the mass, while the central portion, which at 

 first appears to constitute the whole corpuscle, 

 notwithstanding its increase of size, is now to be 

 regarded only as a nucleus, presenting the ap- 

 pearance of a cavity or granular cell, of a form 

 approaching that of a sphere. (See Jig. 460.) 



Cartilage, when it has 

 been subject to the 

 above changes, in the 

 next transition becomes 

 bone. In order to un- 

 derstand this process 

 it will be necessary to 

 bear in mind the fol- 

 lowing points : first, 

 that the enlarged carti- 

 lage corpuscles are ar- 

 ranged in vertical co- 

 lumns; that each co- 

 lumn is surrounded by 

 the intercellular tissue, 

 and that each corpuscle 

 is separated from those 

 above and below by a 

 layer of intercellular 

 tissue; and, lastly, that 

 each corpuscle has dis- 

 tinct parietes with cen- 

 tral nucleus, or cavity, 

 containing granules or 

 having granular parie- 

 tes. Osseous tissue is in all instances developed 

 in the form of minute granules, so the earliest 

 appearance of bone in cartilage is marked by 

 the presence of these spherical granules in the 

 intercolumnar and intercellular tissue, which is 

 thereby increased in density and opacity. This 

 constitutes the first stage in the process of the 

 developement of bone, and may be observed 

 by making a thin section of a bone at the point 

 of junction of the bone and cartilage, where the 

 shaft is connected with the epiphysis. (See 

 fig. 461.) The granular appearance will be 



Fig. 461. 



Section of temporary car- 

 tilage, which has under- 

 gone the last stage towards 

 ossification. 



a, intercolumnar tis- 

 sue ; b, the enlarged pa- 

 rietes of corpuscle ; c, 

 central nucleus of the 

 corpuscle. 



Section of the intercellular or hyaline substance, the 

 corpuscle having been removed. 



Not only are the described changes in form 



Transverse section of temporary cartilage in the first 

 stage of ossification. 



a, a, intercellular tissue ossified ; b, the trans- 

 parent parietes of the enlarged corpuscle ; c, the 

 central nucleus, which in the specimen from which 

 this figure was taken was granular. 



