66 SKELETON. 



which communicates freely with the other arteries of the bones. 

 This membrane is so arranged as to form along the course of 

 the blood vessels small vesicular appendages which contain the 

 marrow, and bear some analogy to a thick bunch of grapes* 

 hanging from the several pedicles of the stem. 



Its nerves are extremely small; they enter by the nutritious 

 foramen, and have been particularly observed by Wrisberg and 

 Klint* They have not been traced ramifying in the substance 

 of the bone, but follow for some distance the course of the prin- 

 cipal arteries. 



With the exception of Mr. Cruikshank's solitary injection of 

 a vertebra, no lymphatics have been observed satisfactorily on 

 this medullary membrane; and such trunks of the external peri- 

 osteum as are supposed to arise from the medullary membrane, 

 have not been traced nearer to it, than the orifice of the nutri- 

 tious canal. 



Some differences exist in the nature of the contents of the 

 medullary membrane; for example, that part of it which is re- 

 flected over the cells in the extremities of the long bones, and 

 in the whole interior of the flat, and of the thick ones, contains 

 a much more bloody and watery marrow, than what is found in 

 the cylindrical cavities of the long bones: the latter, indeed, re- 

 sembles closely, as just stated, common adeps, presenting no es- 

 sential differences from it. These circumstances have given 

 occasion, without a material distinction of texture, to divide the 

 medullary membrane into two varieties. 



That variety contained in the cellular extremities of the long 

 bones, and in the spongy bones generally, is in a superior degree 

 vascular. The part within the meshes of its vessels is, however, 

 so imperfect, that Bichat declared his inability to find it, and 

 that the number of the fine vessels was what gave, fallaciously, 

 the appearance of a membrane; while, in fact, the intervals be- 

 tween them were large, to allow the fat to come into contact 

 with the naked bone. The probability of this deficiency is con- 

 firmed by the circumstance, that no one pretends to have found 

 a membrane in the microscopical pores of the compact substance, 

 yet the existence of fat in it is proved by its becoming greasy 

 when insulated and exposed to heat. It is from the great abun- 

 dance of blood in this variety of the medullary tissue, that the 

 proportion of its adeps is small. 



* Beclard, loc.. ciU 



