STRUCTURE OF THE BOXES. 339 



many ramifications, and but few anastomoses. Secondly, numerous 

 finer nerves penetrate with the numerous bloodvessels into the can- 

 cellated tissue, and ramify in the medulla. And, thirdly, extremely 

 delicate nervous filaments are sent into the compact structure of the 

 epiphyses, in company with the minute arteries by which they are 

 penetrated. The smaller cylindrical bones of the hand and foot 

 present the same conditions as the larger ones just described, except 

 that the nerves are not so regularly divided into epiphysal and dia- 

 physal, on account of the undeveloped condition of the medullary 

 cavities. 



Of the short bones, the vertebrae are most abundantly supplied 

 with nerves ; and especially their bodies. (Kolliker.) They enter 

 anteriorly, posteriorly, and on the sides, in company with the ves- 

 sels, and are distributed to the marrow of the spongy substance. 



In the flat bones as the- scapulae and coxal bones the nerves 

 are very numerous, and enter the bone with the larger vessels before 

 described. In the occipital, parietal, and frontal bones, microscopic 

 nervous filaments enter as far as to the diploe, upon the finer arteries. 



The nerve-fibres thus richly distributed to bone are both cerebro- 

 spinal and sympathetic ; the former constituting about two-thirds 

 of all the fibres, and being 5 oV(j to soW f an i nc h m diameter, 

 (Kolliker?) The periosteal nerves are also, apparently, mainly spinal ; 

 though some participation of the sympathetic cannot, perhaps, be 

 denied in their case, also. 



How the nerves of bone terminate, is not yet decided. They 

 sometimes have Pacinian bodies upon them just before entering the 

 bone-substance. 



The principal function of the nerves of bone seems to be to regu- 

 late the flow of blood and plasma through the part. (Kolliker.) 



The synovial membranes also contain nerves. The ligaments (in 

 man) do not ; and the same is true of the articular cartilages. 



4. The Marrow of the Bones (Medulla). 



Almost all the larger cavities in the bones are filled by a soft r 

 transparent, yellowish or reddish, highly vascular substance, the 

 marrow. It is found chiefly in the medullary canals of cylindrical 

 bones, and in the cancelli of all bones ; though it also enters into 

 the larger Haversian canals of the compact substance. In the shafts 

 of the long bones it appears as a yellow semi-fluid substance, differ- 

 ing essentially in chemical composition from the red kind of marrow 



