DEVELOPMENT OF BONE. 73 



of the canaliculi have become filled with the balsam and 

 rendered invisible. 



Marrow. A long bone, from a rabbit or from a child, 

 should be broken across and a little of the red marrow 

 scooped out and hardened in alcohol. Fragments are 

 then stained in picro-carmine, bits of these are teased, 

 very line, on a slide and mounted in glycerin. 



DEVELOPMENT OF BONE. 



At a certain period of embryonic life no bone-tis- 

 sue is found in the body, the parts where it is finally 

 to be, being occupied either by cartilage or fibrillar 

 connective tissue. Out of these tissues the bone is 

 developed by a process which, though presenting 

 considerable differences in detail in various parts of 

 the body, is yet, in its essential nature, the same in 

 all. We recognize three ways in which bone is 

 developed: I. In the substance of preexisting car- 

 tilage intra-cartilaginous ; 2. beneath the periosteum 

 sub-periosteal ; 3. in the substance of preexisting 

 fibrillar connective-tissue membranes intra-mcm- 

 branons. In all of these modes of bone-formation 

 the new bone seems to be deposited under the 

 influence of certain large, granular, usually spheroidal 

 or cuboidal cells, called osteoblasts. 



i. When bone is formed from cartilage, the latter 

 bears a general resemblance in shape to the finished 

 bone. The first change which we notice in such a 

 cartilage which is about to undergo ossification, is 

 that at a certain point if it be a long bone,, at 



