c BONE. 



beneath ; for, when the earthy matter is extracted by means of an acid, the 

 tissue which remains has all the characters of cartilage. 



As to the mode in which the earthy matter is connected with the animal 

 substance, we know that the combination is very intimate, but the manner 

 in which it is effected is not fully understood ; probably there is a chemical 

 union between the collagenous matter and the earthy salts. 



The periosteum, as already stated, is a fibrous membrane which covers 

 the bones externally. It adheres to them very firmly, and invests every 

 part of their surface, except where they are covered \vith cartilage or con- 

 nected to other bones by tibro- cartilage. According to Kolliker it is com- 

 posed of two different layers ; the outer, consisting of white fibres, and 

 containing occasional fat-cells, is the means of supporting numerous blood- 

 vessels destined for the bone, which ramify in the membrane, and at length 

 send their minute branches into the Haversian canals of the compact sub- 

 stance, accompanied by processes of filamentous tissue derived from, or at 

 least continuous with, the periosteum. The inner layer is made up of 

 elastic fibres ; and frequently presents the appearance of several distinct 

 strata of "elastic membrane." Fine nervous filaments spread out in the 

 periosteum ; they are chiefly associated with the arteries, and for the most 

 part destined for the subjacent bone ; but some are for the membrane 

 itself. 



The chief use of this membrane is evidently to support the vessels going to the 

 bone, and afford them a bed in which they may subdivide into fine branches, and so 

 enter the dense tissue at numerous points. Hence, when the periosteum is stripped 

 off at any part, there is great risk that the denuded portion of the bone will die and 

 exfoliate. The periosteum also contributes to give firmer hold to the tendons and 

 ligaments where they are fixed to bones; indeed, these fibrous structures become 

 continuous and incorporated with it at their attachment. 



The marrow (medulla ossium) is lodged in the interior of the bones ; it 

 fills up the hollow shaft of long bones and occupies the cavities of the 

 cancellated structure ; it extends also into the Haversian canals at least 

 into the larger ones along with the vessels. Like ordinary adipose tissue, 

 it consists of vesicles containing fat, with blood-vessels distributed to them. 

 A fine layer of a highly vascular areolar tissue lines the medullary canal, as 

 well as the smaller cavities which contain marrow ; this has been named the 

 medullary membrane, internal periosteum, or endosteum ; but it cannot be 

 detached as a continuous membrane. Its vessels partly supply the con- 

 tiguous osseous substance, and partly proceed to the clusters of adipose 

 vesicles, among which there is but very little connective tissue, in conse- 

 quence perhaps of their being contained and supported by bone. 



The marrow differs considerably in different situations. Within the shaft of the 

 long bones it is of a yellow colour, and contains, in 100 parts, 96 of fat, 1 of con- 

 nective tissue, and 3 of water. In short bones, and in the cancellated ends of long 

 bones, but especially in the cranial diploe, the bodies of the vertebrce, the sternum, 

 and the ribs, it is red or reddish in colour, of more fluid consistence, and with very 

 few fat-cells. That from the diploe consists of 75 parts of water and 25 of solid 

 matters, which are chiefly albumen, fibrin, extractive and salts, with mere traces of 

 fat. While, however, the fat-cells are scanty in the red-coloured marrow, it contains 

 minute tyundislv $u elected, cells the proper marrow-cells of Kolliker. These, which 

 include BO, fat n corsespoiicfin character jwhb, th,e cells found in the articular ends of 

 long bones' affecVed wit hvperceijr.iai' tk r eji)cc?ur normally in the cranial bones, ver- 



