THE OSSEOUS SYSTEM. 313 



same way. At one or more points (puncta ossificationis), in their inte- 

 rior, a deposition of calcareous matter commences, simultaneously with 

 a change in the cartilaginous elements ; which transformation proceeds 

 on some or on all sides, continually converting additional portions of the 

 cartilage into bone. Whilst this is going on, the cartilage, in most cases, 

 ceases to grow in one direction, and, consequently, is there soon entirely 

 converted into bone, whilst in others its growth continues, so that a new 

 cartilaginous, plastic material is furnished for the progressive increase 

 of the bone, which material, as in the epiphyses of the cylindrical bones, 

 is sometimes developed into distinct ossific centres or nuclei. When the 

 whole of the cartilage has been converted, and its perichondrium become 

 periosteum, the bone does not cease to enlarge, but a new and peculiar 

 mode of formation is now set up, in all these places, until its growth is 

 completed. This consists in the ossification, from that surface which is 

 in contact with the bone, of an organized, soft, plastic material, which 

 is deposited on the inner surface of the highly vascular periosteum, and 

 in proportion as this conversion into bone takes place on the one side, 

 fresh, fluid materials for it are afforded by the periosteum on the 

 other. 



103. Changes in the ossifying Cartilage. The active vegetative 

 process in the cartilage-cells when ossification is going on, depends upon 

 this, that the cells which were hitherto of small size, and contained but 

 few secondary cells, begin to grow, and successive generations of cells 

 to be produced in them, as may, also, be seen at the ossifying margins 

 of bones already existing, in which situation larger cells may be noticed 

 close to the bone, and others, which are smaller in proportion to their 

 distance from it. All the cells which are engaged in the incipient for- 

 mation of the bone, present clearer and, less frequently, granular con- 

 tents, a distinct, vesicular, round nucleus, with nucleolus and readily 

 distinguishable walls ; they are very quickly altered, however, on the 

 addition of water, acetic acid, alcohol, and by drying, &c., so that the 

 contents contract around the nucleus, and form a roundish, elongated, 

 irregular, even stellate, granular, opaque body (cartilage-corpuscle of 

 authors). Their size and mode of grouping vary, not inconsiderably, 

 according to age and situation. With respect to the former, they exhibit 

 during embryonic life a constant increase, whilst after birth they appear 

 to retain a uniform size ; and, as regards the latter, it may be stated as 

 a law, that where the ossification of the cartilage proceeds in one direc- 

 tion only, the cells, at the osseous border, are disposed in rows. This is 

 most distinctly seen, as has been long well known, in the extremities of 

 the diaphyses of the larger cylindrical bones, where the rows of cells are 

 very prettily arranged in parallel lines close together, and are of con- 

 siderable length ; it is also evident in the other long bones, as well as in 



