2 Anatomy of Skeleton 



plane, and the ligament must be attached practically in the axis round which the movement 

 takes place. 



The bones constitute the larger part of the skeleton. Bone is extremely hard, but at the same 

 time exhibits a small amount of elasticity and toughness. It differs from mere calcification of 

 cartilage, in that it has a definite organised structure (Fig. i), but it can be looked on as composed 

 of animal or organic matter impregnated with earthy salts : analysis gives (roughly) about one- 

 third or less of animal matter and the rest as 

 mineral matter. The former gives toughness 

 and the latter hardness to the composite result. 



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FIG. I . Section of bone under a low power. Each 

 Haversian system consists of a central canal 

 containing vessels and surrounded by a 

 number of concentric lamellae of bony tissue, 

 between which are minute lacunae which 

 communicate by very fine channels and hold 

 cells (bone-corpuscles). Compact bone is com- 

 posed of an aggregation of such systems. 



Fresh bone possesses a pinkish hue on 

 the surface, which is covered by a fibrous 

 periosteum of variable thickness. Bone 

 exists in two states in the body, termed, 

 according to the appearance it presents, 

 compact and cancellous ; examples of both 

 sorts of bone can be seen in a section 

 along a bone of any size. Complete 

 Haversian systems only occur, of course, 

 in the compact bone, which is made up 

 of a series of the systems (Fig. 2). 



The shaft of a long limb bone is com- 

 posed of compact bone which makes a 

 shell that is hollow internally : this is the 

 medullary cavity, and it is walled directly by the compact shaft-wall in the middle of 

 the bone, but at each end cancellous tissue appears and occupies the cavity. The 

 medullary cavity and the interstices of the cancellous bone are filled with very vascular 

 marrow, of which two distinct varieties are found (a) yellow marrow, found in the 

 shafts of long bones, and containing about 96 per cent, of fat, and (b) red marrow, 

 occurring in the articular ends of the long bones and elsewhere and containing 75 

 per cent, of water, with very little fat and a considerable amount of organic solids. 



The skeleton comprises an appen- 

 dicular skeleton of the limbs as well as 

 an axial skeleton of the trunk. 



The various bones of these parts 

 are divided, according to their shape 

 and appearance, into short, long, flat, 

 and irregular. 



Many and various names are given 

 to the different markings and irregu- 

 larities seen on bones : thus a hole in a 

 bone may be termed a foramen, canal, 

 or, in certain cases, a meatus, hiatus, 

 or (aquae] ductus. Prominences project- 

 ing more or less from the general 

 level are called processes, trochanters, 

 tuberosities, protuberances, tubercles, and 

 spines, or, if more linear in disposition, ridges, spines, crests, or lines. Depressions 

 on the surfaces of bones may be fossa, cavities, fossettes, or fovece ; if more linear in 

 direction, grooves or sulci ; if a large cavity exists in a bone it may be described as a 

 sinus, cell, or antrum. 



FIG. 2. Diagram of a section of an end of a long 

 bone (a) and a short bone (6) to show the arrange- 

 ment of cancellous and compact tissue in them. 



