CARTILAGE. BONE. TEETH. 33 



brane, is incorrect. These names have been applied 

 to the scattered fasciculi of connecting tissue by which 

 the blood-vessels and fat cells of the marrow are sup- 

 ported. 



Marrow is found only in the cancelli and medul- Marrow, 

 lary canals of bone ; neither the Haversian canals 

 nor the canaliculi contain it. In the foetus it is of a 

 reddish color and possesses some consistency ; in the 

 adult it is met with in this form only in the smaller 

 cancelli of spongy bone, and in short and flat bones ; 

 in the medullary canals of long bones, and in the 

 larger cancelli of their spongy substance, it is yellow 

 in color and almost diffluent. Thus, there are two 

 varieties of marrow, which differ in their histologi- 

 cal elements as well as in their physical properties. 

 The red, or foetal marrow, is made up of an aggre- 

 gation of spherical cells, each containing fine granular 

 matter and one large nucleus. Some of these cells have 

 several nuclei, and attain a large size ( T Vth to T Vth 

 of a line). It is worthy of remark, in passing, that 

 the cells of foetal marrow' are identical in appearance 

 with certain forms of so-called cancer cells. This 

 variety of marrow is richly supplied with blood-ves- 

 sels, which traverse its substance, accompanied by 

 delicate filaments of connecting tissue. 



The cells of yellow marrow are nothing more than 

 vesicles filled with liquid *fat, or ordinary fat cells. 

 In some of them the nucleus can be still recognised, 

 and others again resemble so closely the cells of foetal 

 marrow as to suggest a series of transitional changes, 

 by which it is rendered probable that the ordinary 

 yellow marrow is nothing more than foetal marrow. 



