DEVELOPMENT OF BONES. 67 



The second variety of medullary membrane is displayed in 

 the cells and cylindrical cavity of the diaphysis or body of the 

 long bones. Its membranous cells communicate freely with one 

 another when the membrane is entire; but, according to the ob- 

 servations of Bichat, not with such as are in the epiphyses of the 

 bones; and the line of demarkation is abrupt and well defined. 

 This is proved by attempts to inflate the one from the other; the 

 air, in such cases, passes with great difficulty. The texture of 

 this medullary membrane, from its extreme delicacy in a natural 

 state, is rather obscure, but it is occasionally well developed in 

 disease. Its sensibility has not been very apparent in such 

 cases of amputation as I have seen, though it is said, by some, 

 to be extremely exquisite. In whatever degree its sensibility 

 exists in different subjects, it is always more apparent in the 

 middle than near the extremities of the long bones; which may 

 be accounted for by its nerves always entering at the nutritious 

 foramen, and extending from thence towards the extremities. 



The medullary membrane, besides its use in secreting the 

 marrow, is highly serviceable to the nutrition of the bones, as 

 proved in the experiments of Trojat, who, by destroying it, 

 produced their death, and an artificial necrosis, which was cured 

 in the usual way by a new secretion of bone from the perios- 

 teum. The marrow which it contains in the adult is not per- 

 ceptible in the foetus. Moreover, the quality of this marrow is 

 varied by disease; in consumption, dropsy, and other ailments 

 attended with great emaciation, a considerable part of it is ab- 

 sorbed, and a serous fluid deposited in its place; a circumstance 

 well known to those who clean skeletons. 



CHAPTER III. ; 



ON OSTEOGENY. 

 SECT. I. OF THE DEVELOPMENT OF THE BONES. 



AT birth, though the skeleton is sufficiently solid to preserve 

 the shape of the individual, yet it is very imperfect in many 



