MAEROW, 91 



The animal basis is here, however, of a totally different nature from 

 that of the 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 eflFected is not fully understood ; probably 

 there is a chemical union between the collogenous 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 in- 

 vests every part of their surface, except where they are covered with 

 cartilage or connected to other bones by fibro-cartilage. According to 

 KulHker it is composed of two difi'erent layers ; the outer, consisting of 

 white fibres, and containing occasional fat-cells, is the means of sup- 

 porting numerous l)lood-vessels destined for the bone, which ramify in 

 the membrane, and at length send their minute branches into the 

 Haversian canals of the compact substance, accompanied by processes 

 of filamentous tissue derived from, or at least continuous with, the 

 periosteum. The inner layer is made up of clastic fibres ; and 

 frequently presents the appearance of several distinct strata of " elastic 

 membrane." Between those, however, and the proper osseous tissue 

 there is, in the vouug bone at least, a fibrous stratum containing a 

 number of granular corpuscles (fig. 62, c). Fine nerves 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. By treating the membrane with nitrate of 

 silver, lymphatics are discovered in it accompanying the blood-vessels, 

 and, as in other aponeurotic structures, extensive epithelioid markings, 

 covering a great part of the surface, are brought into view. 

 * 



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

 hone, 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 iDeriosteum is 

 stripped ofif 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 incorj^orated with it at their attachment. It.s 

 relation to the growth of bone will be refeiTed to later on. 



The marrow {mrduUa ossiiim) 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. 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 continuons membrane. Its vessels partly supply 

 the contiguous osseous substance, and partly proceed to the clusters 

 of adipose vesicles, among which there is but very little connective 

 tissue, in consequence 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 the character of ordinary adipose tissue. 



