

BONE 



87 



them abundant, while in the cancellous tissue the spaces are large and the solid 

 matter is in smaller quantity. 



Bone during life is permeated by vessels, and is enclosed, except where it is 

 coated with articular cartilage, in a fibrous membrane, the periosteum, by means 

 of which many of these vessels reach the hard tissue. If the periosteum be stripped 

 from the surface of the living bone, small bleeding points are seen which mark the 

 entrance of the periosteal vessels; and on section during life every part of the 

 bone exudes blood from the minute vessels which ramify in it. The interior of 

 each of the long bones of the limbs presents a cylindrical cavity filled with marrow 

 and lined by a highly vascular areolar structure, called the medullary membrane. 



I 

 I 





Periosteum. The periosteum adheres to the surface of each of the bones in 

 nearly every part, but not to cartilaginous extremities. When strong tendons or 

 ligaments are attached to a bone, the periosteum is incorporated with them. It 

 consists of two layers closely united together, the outer one formed chiefly of 

 connective tissue, containing occasionally a few fat cells; the inner one, of elastic 

 fibers of the finer kind, forming dense membranous networks, which again can be 

 separated into several layers. In young bones the periosteum is thick and very 

 vascular, and is intimately connected at either end of the bone with the epiphysial 

 cartilage, but less closely with the body of the bone, from which it is separated by 

 a layer of soft tissue, containing a number of granular corpuscles or osteoblasts, by 

 which ossification proceeds on the exterior of the young bone. Later in life the 

 periosteum is thinner and less vascular, and the osteoblasts are converted into an 

 epithelioid layer on the deep surface of the periosteum. The periosteum serves 

 as a nidus for the ramification of the vessels previous to their distribution in the 

 bone; hence the liability of bone to exfoliation or necrosis when denuded of this 

 membrane by injury or disease. Fine nerves and lymphatics, which generally 

 accompany the arteries, may also be demonstrated in the periosteum. 



Marrow. The marrow not only fills up the cylindrical cavities in the bodies of 

 the long bones, but also occupies the spaces of the cancellous tissue and extends 

 into the larger bony canals (Haversian canals) which contain the bloodvessels. 

 It differs in composition in different bones. In the bodies of the long bones the 

 marrow is of a yellow color, and contains, in 100 parts, 96 of fat, 1 of areolar tissue 

 and vessels, and 3 of fluid with extractive matter; it consists of a basis of connective 

 tissue supporting numerous bloodvessels and cells, most of which are fat cells 

 but some are "marrow cells," such as occur in the red marrow to be immediately 

 described. In the flat and short bones, in the articular ends of the long bones, 

 in the bodies of the vertebrae, in the cranial diploe, and in the sternum and ribs 

 the marrow is of a red color, and contains, in 100 parts, 75 of water, and 25 of solid 

 matter consisting of cell-globulin, nucleoprotein, extractives, salts, and only a 

 small proportion of fat. The red marrow consists of a small quantity of connective 

 tissue, bloodvessels, and numerous cells (Fig. 72), some few of which are fat cells, 



1 Indicates stresses with the grain, i. e., when the load is parallel to the long axis of the material, or parallel to the 

 direction of the fibers of the material. 



2 Indicates unit-stresses across the grain, i. e ., at right angles to the direction of the fibers of the material. 



