358 SPECIAL HISTOLOGY. 



first small, and more internally, larger, come into view, the 

 whole relations of which show most convincingly that they do 

 not originate in any development of the existing elements. 

 They have an extremely irregular contour, are oval, or roundish 

 and angular, and for the most part broader than the cartilage- 

 cells, appearing to be eaten out, as it were, in the substance of 

 the bone, and involving severally the compact tissue, matrix, 

 and bone-cells. When the borders and limitary surfaces of 

 these spaces are closely regarded, it is, in many instances, easy 

 to notice bone-cells more or less removed, half projecting from, 

 or buried in the wall, and between them projections of the 

 ossified matrix, so that no doubt can any longer be entertained 

 with respect to the origin of the cavities. It must be confessed 

 that there is as little to be stated, in this case, as in that of the 

 origin of the analogous cartilage-canals, and the further 

 development of the canaliculi of the bone-cells, with respect to 

 the mode in which this absorption takes place ; and the process 

 is even still more inexplicable, because, allowing that it 

 really does take place, there would then exist in the ossifying 

 bone, at the same time and almost in immediate contiguity, 

 a formation of bone and a resolution of the tissue, but very 

 little less energetic. The above-described mode of formation 

 of the cancelli, nevertheless, is a morphological fact, and con- 

 sequently, the explanation of such a curious phenomenon 

 becomes a problem to be solved by chemistry and physiology. 

 As in the diaphyses, so in the ossification of all the other 

 cartilages, medullary spaces are formed by the resorption of 

 the inner portions of that part which is half ossified. But it must 

 be stated, that these spaces do not present the same form, 

 direction, and size in every bone; though with respect to this, 

 it is unnecessary to offer any special remarks, since the 

 relations of this primitive spongy substance are, in the main, 

 the same as they are afterwards. Still, it may be remarked, 

 that in many bones, solitary spaces are apparently developed 

 immediately from cartilage-canals, seeing that some at 

 least of the latter, at the limit of ossification, communicate 

 directly with the spaces in the bone; and, moreover, that not 

 unfrequently, cartilaginous elements not yet wholly converted 

 into bone-cells, are drawn into the process of resolution. 



The medullary cavities, however they arise, are filled with a 



