326 SPECIAL HISTOLOGY. 



form of cribriform lamellae around the ossific-nuclei formed from carti- 

 lage, continue to be produced so long as the general growth of the bone 

 goes on, essentially in the same way, constituting the material by which 

 it increases in thickness ; but at the same time, more or less important 

 changes are set up in them ; the most considerable of which take place 

 in the large cylindrical bones. In these, we find, more distinctly indeed 

 after birth, that a large cavity is gradually formed in the interior, which 

 at first contains foetal medulla-cells, and afterwards perfectly formed 

 medulla. This medullary cavity is formed, in exact analogy with- the 

 medullary spaces described in the preceding paragraphs, by the solution 

 of the osseous tissue of the shaft; at first, only of that which is formed 

 from the primitive cartilaginous rudiment, but soon, also of that deposi- 

 ted from the periosteum upon the former, its development proceeding in 

 a remarkable manner, as long as the general growth of the bone con- 

 tinues. Whence it comes to pass, that, as at the ends of the diaphyses, 

 so also on its surfaces, whilst new bone is continually deposited exte- 

 riorly, that which is already formed is as continually absorbed in the 

 interior ; and in fact these two processes are so combined, that the bone, 

 during its development is, in a certain measure, several times regenera- 

 ted, and, for instance in the humerus of the adult, does not contain an 

 atom of the osseous tissue which existed at the time of birth, nor does 

 the bone at that period contain any of the tissue of which it was con- 

 stituted in the embryo at three months. These conditions will be 

 rendered most distinctly intelligible, and especially with respect to the 

 periosteal and cartilage layers, by means of a diagram (Fig. 134) which 

 I have for a long time employed in my lectures. If, in this figure, we 

 compare the primordial bone E E with the almost complete bone E 4 E 4 , 

 it is apparent, that in the longitudinal growth of the diaphysis of the 

 latter on both sides, at the expense of the continually growing epiphy- 

 sal cartilage, an elongated cone of osseous substance, 1, 2, I 1 2 1 , and 3, 

 4, 8 1 , 4 1 , is produced, to which, ultimately, the epiphysal nuclei E 4 E 4 , 

 also originating in the cartilage, are joined, whilst, to increase its thick- 

 ness, the tubular layer P, P 1 , P 2 , P 3 , which are constantly increasing in 

 length and, in the middle, in thickness, are applied to it. In a cylin- 

 drical bone of this kind consequently, the entire portion formed from 

 cartilage, presents a figure of a double cone with rounded bases ; and 

 that formed from the periosteal layers, 1, '2, 3, 4, P 3 , and I 1 , 2 1 , 3 1 , 4 1 , 

 P 3 , the form of an elongated tube thickest in the middle, and resem- 

 bling an elongated vertebra of a Fish, with conically hollowed, terminal 

 surfaces. The articular cartilage C, is the unossified portion of the 

 epiphysal cartilage, and the medullary cavity which is not shown in the 

 figure (it may be supposed to be indicated pretty nearly by the outlines 

 of the fourth bone E 3 E 3 ), is formed by the resorption of the entire 



