BOXE. 45 



BONE. 



Structure and Physical Properties of Bone. Bone is one of the hardest struc- 

 tures of the animal body ; it possesses also a certain degree of toughness and 

 elasticity. Its color, in a fresh state, is of a pinkish white externally, and deep 

 red within. On examining a section of any bone, it is seen to be composed of 

 two kinds of tissue, one of which is dense and compact in texture, like ivory ; 

 the other consisting of slender fibres and lamellae, which join to form a reticu- 

 lar structure ; this, from its resemblance to lattice- work, is called cancellous. 

 The compact tissue is always placed on the exterior of a bone ; the cancellous 

 tissue is always internal. The relative quantity of these two kinds of tissue 

 varies in different bones, and in different parts of the same bone, as strength or 

 lightness is requisite. Close examination of the compact tissue shows it to be 

 extremely porous, so that the difference in structure between it and the cancel- 

 lous tissue depends merely upon the different amount of solid matter, and the 

 size and number of the spaces in each ; the cavities being small in the compact 

 tissue, and the solid matter between them being abundant ; whilst in the can- 

 cellous tissue the spaces are large, and the solid matter in smaller quantity. 



Bone during life is permeated by vessels, and is inclosed in a fibrous mem- 

 brane, the periosteum, by means of which most 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 ves- 

 sels ; and on section during life every part of the bone will be seen to exude 

 blood, from the minute vessels which ramify in the Haversian canals. The 

 interior of the bones of the limbs presents a cylindrical cavity filled with mar- 

 row, and lined by a highly vascular areolar membrane, the medullary mem- 

 brane or internal periosteum. The larger Haversian canals are also filled with 

 marrow. 



The periosteum adheres to the surface of the bones in nearly every part, ex- 

 cepting at their cartilaginous extremities. Where strong tendons or ligaments 

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

 of two layers closely united together; the outer one formed chiefly of con- 

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

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

 again separated into several layers (Kolliker). In young bones the periosteum 

 is thick, and very vascular, arid is intimately connected at either end of the bone 

 with the epiphysial cartilage, but less closely with the shaft, from which it is 

 separated by a layer of soft blastema, in which ossification proceeds on the ex- 

 terior of the young bone. Later in life the periosteum is thinner, less vascular, 

 and more closely connected with the adjacent bone, this adhesion growing 

 stronger as age advances. The periosteum serves as a nidus for the ramifica- 

 tion of the vessels previous to their distribution in the bone ; hence the liability 

 of bone to exfoliation or necrosis, when, from injury, it is denuded of this 

 membrane. 



The marrow differs in composition at different periods of life, and in different 

 bones. In young bones, it is a transparent reddish fluid, of tenacious consist- 

 ence, free from fat ; and contains numerous minute roundish cells with many 

 nuclei. In the shafts of adult long bones, the marrow is of a yellow color, and 

 contains, in 100 parts, 96 fat, 1 areolar tissue and vessels, and three of fluid 

 with extractive matters ; whilst, in the flat and short bones, in the articular 

 ends of the long bones, in the bodies of the vertebrae, in the base of the cranium, 

 and in the sternum and ribs, it is of a red color, and contains, in 100 parts, 75 

 water and 25 solid matter, consisting of albumen, fibrin, extractive matter, salts, 

 and a mere trace of fat. The red marrow is said by Kolliker to consist of a 

 small quantity of areolar tissue and numerous medullary cells, and fat-cells 

 with a large quantity of fluid. 



