FORMATION OF THE MARROW OF BONES. 453 



with age. However, as I have already pointed out to 

 you, there are no sacs in the areolse of the bones, but a 

 continuous tissue, the medullary tissue, which fills the 

 medullary spaces [cancelli] and cavities and belongs to 

 the class of connective tissues, although it considerably 

 differs from ordinary connective tissue. We have there- 

 fore here to deal, as you see from this simple fact, with 

 a substitution of tissues. As osseous tissue* is formed 

 out of periosteum and cartilage, so marrow is formed 

 from osseous tissue, and the development of a bone 

 consists not merely in the formation of osseous tissue, 

 but it presupposes that the series of transformations 

 goes beyond the stage of bone, and that medullary 

 tissue is. then produced. Medullary tissue therefore 

 constitutes in some sort the physiological termination of 

 the formation of bone as an organ. 



However simple this view may be, still it furnishes us 

 with a picture of the growth and history of bone dif- 

 ferent from the traditional one. Formerly, observers 

 nearly always contented themselves with viewing the 

 matter much in the same light that osteologists are wont 

 to do ; they took a macerated bone, examined it when 

 divested of all its soft parts, and built up the processes 

 accordingly. It is, however, necessary that the relations 

 should be traced in the moist, living healthy or diseased 

 bone, and that one should pay attention not only to the 

 development of bone upon the outside from the growing 

 layers of the cartilage and periosteum, but also to that 

 of the medulla on the inside, as the ultimate product of 

 the development in this class of tissues, even if it be 

 not the noblest one. The most important and really 



* Osseous tissue (tela ossea, tissu osseux) = bone corpuscles -f- calcified inter* 

 cellular substance. Bom as an organ = osseous tissue -|- medullary tissue -f- peri- 

 osteum -f- vessels -f- nerves. Osseous substance is sometimes taken to mean a por- 

 tion of bone considered as an organ. From a MS. Nott by the Author. 



