20 PROCEEDINGS OF THE AMERICAN ACADEMY 



or, nccorditifT to Owen and others, radiations of its nucleus ? My own 

 opinion is diflerent from either, and for the following reasons. In the 

 firet place, the canaliculi do not begin to form until calcareous matter 

 J.3 deposited, and, as the cell-npembrane is then either filled with cal- 

 careous matter, or partially absorbed, it could not well send out pro- 

 longations. Moreover, these last are often of such a length, and so 

 branch and rebranch upon themselves, that such a mode of formation 

 seems hardly possible. To me it appears most probable that they are 

 the channels of escape of aeriform matters from the interior of the 

 cell. For the cell, situated in the midst of an ossifying mass, would 

 retain for some time its animal matter, and this last would ultimately 

 give rise to gases seeking their escape in every direction by percolat- 

 ing the surrounding semi-solid mass. Canaliculi would thus be formed, 

 and these, converging towards the nearest outlet, have therefore been 

 rightly called ' converging tubuli.' 



" During these phases of formation, some of the nuclei of the 

 cartilage-cells, or even whole other cells of a small size, may not be 

 dissolved, but become ossified as such. They are then found as cell- 

 like corpuscles scattered through the osseous tissue. It is in this way 

 that 1 account for the occasional presence, in the spongy tissue of the 

 long bones, of small spherical bodies, first discovered in 1849 by Dr. 

 O, VV. Holmes of this city. 



" Such appear to be the processes of formation of the compact 

 tissue of the bones of the higher Vertebrata, as I have studied them in 

 foetal goats. 



" The whole process is simply one of substitution, with that con- 

 traction and modification of form which necessarily ensues when a 

 soft is replaced by a sclerous tissue. 



" This process of substitution is carried out everywhere the same, 

 there being, however, variations in some steps of its progress in the 

 different kinds of bones. The spongy nature of the internal or mid- 

 dle portions of some bones appears to be produced by the absorption, 

 by numerous vessels there situated, of the lighter portion of the primi- 

 tive cartilaginous base, and a consolidation of the remaining portion 

 towards the periphery. 



" This is a point, however, having an unusual teleological bearing, 

 for by such process bones possess the greatest combined strength and 

 lightness attainable with the same amount of material. 



- These phases of formation just described belong especially to the 



