THE CONNECTIVE SUBSTANCE GROUP. 97 



cles that line them are called osteoblasts. Whether or not they 

 are identical with the cartilage-corpuscles, or belong to the 

 budding marrow-processes, seems to be a matter of doubt. 

 Klein intimates that the cartilage-corpuscles disintegrate. Ran- 

 vier has seen no proof of it. It is probable that some of the 

 cartilage-corpuscles persist, certainly to a limited extent, 

 and preside over the remains of the calcified cartilage. The 

 bulk of the new bone is made up, however, of new material 

 which is deposited under the form of concentric lamellae about 

 the marrow cavities, most likely by a proliferation of the 

 osteoblasts. 



These changes may all be observed to advantage in the 

 specimen just mentioned, and the successive gradations of the 

 process can be conveniently magnified, so as to be easily seen, 

 by making sections obliquely to the surface of the bone. With 

 a low power the specimens will have uncommon beauty, as the 

 corpuscles take the carmine well, while the interstitial tissue is 

 of a bright, transparent grass-green. 



In a vertical section of a long bone, while the process is 

 essentially the same, there are some modifications in the suc- 

 cessive steps. Thus the spongy bone of the epiphysis en- 

 croaches on the cartilage, causing it to be absorbed in the man- 

 ner already described, but the intermediary cartilage, lying 

 between the epiphysis and diaphysis, is seen to have its cor- 

 puscles arranged in long lines parallel with the axis of the 

 bone ("step-ladders"). The bone meshes of the encroaching 

 bone are also shaped in correspondence with the cartilage cap- 

 sules, that is, they are long and narrow. 



Formation of bone through the medium of cartilage. The 

 successive changes in this species of bone development have 

 been best described by Klein. According to him the hyaline 

 cartilage that is destined to prepare the way for bone is covered 

 with perichondrium, consisting like the periosteum of two 

 layers. This membrane does not at first contain mature fibrous 

 tissue, but merely the rudiments of it, under the form of spin- 

 dle-shaped corpuscles ; its internal layer, however, is early pro- 

 vided with spherical corpuscles, the future osteoblasts, and is 

 rich in vessels. 



Subsequently this osteogenetic envelope puts out processes 

 (periosteal processes, Virchow) that penetrate into the carti- 

 lage-capsules, which, melting as the external growth makes its 

 7 



