142 GENERAL ANATOMY. 



These prolongations are supported by the filaments and lamina 

 of the reticular substance, in those places where it exists. 



174. The composition of the medullary membrane, is prin- 

 cipally owing to the vessels that are ramified in the interior of 

 the canal, and which are supported by an extremely soft and 

 hardly visible tissue : this membrane, in this respect, greatly 

 resembles the pia-mater or the epiploon, and appears formed 

 like them, by the cellular tissue belonging to the sheaths of 

 the vessels. An artery and vein penetrate into the medullary 

 canal, and as soon as they have entered it, divide in two 

 branches, whose ramifications extend to the two extremities 

 of the bones, and communicate with the numerous and large 

 vessels of their extremities. The lymphatic vessels have been 

 followed to the entrance of the medullary cavities only. Suc- 

 cessful injections, on the contrary, show a multitude of colour- 

 ed filaments in the canal of long bones. The nerves of this 

 canal, whose existence has been denied, may be easily traced. 

 Soemmering, it is true, thinks that these nerves are destined 

 for the artery only. These nerves have been particularly 

 studied by Wrisburg and Klint. The medullary tissue is then 

 essentially composed, 1st, of an arterial and veinous net-work, 

 and probably of one of lymphatic vessels also: 2d, of a nervous 

 plexus destined either for the artery, or the artery and other 

 parts; 3d, of the cellular sheaths peculiar to these parts that 

 give out fibrilli, whose re-union form a sort of incomplete, 

 fringed, membrane. To this must be added vesicles, that are 

 very apparent, but in the recent subject only, as in others they 

 become much less distinct, owing to the rapidity with which 

 the marrow becomes fluid. These vesicles are in every re- 

 spect precisely similar to those of the adipose tissue in gene- 

 ral; they have the same volume, and the same connexion with 

 the blood-vessels, to which they appear appended. Grutzma- 

 cher, thinks that the texture of the marrow, and that of the fat 

 generally, is areolar like the common cellular tissue, and not 

 vesicular. The spongy extremities of the long bones contain 

 a great number of vessels; but their membrane is less dis- 

 tinct than that of the middle of the same bones. There ap- 

 pears to be vesicles there, similar to those of the medullary 



