TISSUES OF THE BODY. 



253 



ilie first to fall a prey to this re-solution. If we still keep to the 

 diaphysis of the cylindrical bones, we see the walls of the capsules of one 

 row, as well as the small amount of intercellular matter between them, 

 becoming dissolved, by which long narrow cavities with wavy contour 

 are produced (fig. 241, d). Then again, owing to the fact that other 

 neighbouring parts of the ground-mass of the cartilage become a prey to 

 advancing liquifaction, numerous communications are formed between 

 adjacent sinuses (d, above). If we now turn to an epiphysis (fig. 242) 

 or a short bone, we are struck by the fact that the re-solution takes 

 place irregularly in all directions, starting from the bone already formed. 

 The consequence of this is, that the medullary sinuses form a system* of 

 irregular tortuous cavities, the tracing of which is a matter of difficulty, 

 and whose arms not unfrequently simulate closed medullary spaces, when 

 the entrance has come away in making the preparation (fig; 242, a [to the 

 right and above], &.) 



The contents of the cavities formed in this manner are of great import- 

 ance, supplying the substratum for future processes, or, as we might express 

 it generally, constituting the foetal medulla. 



The latter (fig. 244), a soft reddish substance, shows moderately small 



Fig. 243. Tranvci se section from the upper portion of 

 the femur of a human embryo of eleven weeks old. 

 o, residue of cartilage ; 6, coating of osseous tissue. 



Fig. 244. Medullary cells of cartilage, a, 

 from the humerus of a human foetus of 

 five months old ; 6, from the same bone 

 of an infant; c, fusiform cells; rf, for- 

 mation of the fat cells of the nedulla; 

 e, a cell filled with fat globules. 



roundish cells, measuring 0*0129-0*0257 mm. (a), of a very primitive ap- 

 pearance, reminding one of embryonic elements or lymphoid cells. They 

 possess more or less granular contents and a single or double nucleus. 

 These are held by some to be either immediate or more remote descend- 

 ants of the cartilage cells, which have found their way into the cavities, 

 commencing with the absorption of the capsules, there undergoing 

 segmentation, and thus producing new generations. However, though 

 we do not wish to deny the possibility of such an origin, the greater part 

 of these (perhaps contractile) cells of the cartilage medulla has certainly 

 another source. They are young formative-cells, entering the cartilage 

 cavities with the advancing blood-vessels of the internal layers of the 

 perichondriurn and periosteum (Gegenbaur, fret/, Rottett, Stieda). They 

 may be regarded as emigrated lymphoid cells of the blood. 



The further destiny of these cells is very various. Some of them become 

 fusiform (c c), and form very early. scattered connective-tissue fibres, which 

 traverse the tissue, which probably contains mucin. Other cells preserve 

 the old lymphoid form. In the red medulla the latter are to be seen the 



