3G4 SPECIAL HISTOLOGY. 



The periosteal layers, which, agreeably to what has been stated, 

 are from the first deposited in the form of cribriform lamellae 

 around the ossific-nuclei formed from cartilage, 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 deposited from the periosteum upon the former, its de- 

 velopment proceeding in a remarkable manner, as long as the 

 general growth of the bone continues. Whence it comes to pass, 

 that, as at the ends of the diapbyses, so also on its surfaces, 

 whilst new hone is continually deposited exteriorly, 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 

 regenerated, 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 constituted 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. 13 1) 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* E 1 , it is apparent, that in the longitudinal growth of 

 the diaphysis of the latter on both sides, at the expense of the 

 continually growing epiphysal cartilage, an elongated cone of 

 osseous substance, 1, 2, l 1 2 1 , and 3, 4, 3 1 , 4 1 , is produced, to 

 which, ultimately, the epiphysal nuclei E 4 E*, also originating 

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

 ness, the tubular layers P, P 1 , P 3 , P°, which are constantly 

 increasing in length and, in the middle, in thickness, arc applied 



