310 SPECIAL HISTOLOGY. 



presents, besides vessels and nerves, connective tissue, fat -eel Is, 

 free fat, a fluid, together with, lastly, peculiar minute cells, 

 marrow-cells. Connective tissue and fat are universally pre- 

 sent, though in very various quantities. The former, on the 

 surface of the larger medullary masses of the diaphyses, is of 

 rather firmer consistence, but cannot properly be described as 

 a medullary membrane (endosteum, periosteum internum), 

 because it does not admit of being separated as a continuous 

 structure. In the interior of the marrow in the spongy 

 bones, scarcely any connective tissue can be detected except in 

 the larger masses of it, whilst in the diaphyses, this tissue can 

 be readily demonstrated as a very lax and delicate, areolated 

 structure, containing the fat and supporting the vessels and 

 nerves. Its elements correspond with those of the lax con- 

 nective tissue (vid. § 24) ; although, as far as I have seen, it 

 does not contain anv elastic filaments. Fat-cells of 0*01 6 — 

 O032'", not unfrequently with a distinct nucleus, occur in 

 large quantities in the yellow, more dense marrow, quite as 

 abundantly as in the panniculus adiposus, but for the most 

 part not aggregated into distinct lobules. In the reddish 

 marrow, when expressed, they are more rare; and in the red 

 pulp of the bodies of the vertebrse and of the flat cranial bones, 

 they occur only in very minute, scanty accumulations, or 

 altogether isolated, to which circumstance, according to Ber- 

 zelius, is owing the small quantity of fat in the diploe. In 

 dropsical marrow these cells are frequently only 

 c half filled with fat, or with but one or more 

 ^ globules, containing, besides, a large quantity of 

 a serum ; and in hyperemia of the bones, they 

 appear occasionally to be diminished in size, 

 and occasionally elongated and fusiform. Free 

 fat-ylobules, and a clear or yellowish fluid, are 

 often met with in the softer kinds of marrow, 

 and frequently in considerable quantity. That the former 

 have not been set free from cells, in the preparation of the 

 specimen may be satisfactorily shown, but it must remain 

 uncertain whether or not they are to be referred to cells that 

 have ceased to exist. Lastly, there occur, together with some 



Fig. 120. Two fat-cells from the marrow of the human femur ; a, nucleus ; b, cell- 

 membrane; c, oil ; x 350 chain. 



