THE ANATOMY OF THE HUMAN 



SKELETON 



CHAPTER I 

 PRELIMINARY 



The SKELETON constitutes the framework on which the soft tissues of the body are 

 supported, enabling them to retain their definite position in the body and, in the case 

 of the limbs, affording a strong system of levers by means of which the muscles may 

 change the situation of the body as a whole or of its various parts. To serve such 

 functions the skeleton must be strong yet elastic, and must permit of movement 

 without effort yet also without any serious lessening of its strength. These ends are 

 attained by dividing up the skeleton into numerous constituent pieces, by making 

 these of very strong and hard yet somewhat elastic material (bones and cartilages), 

 and by connecting these bones and cartilages by means of joints or articulations, at 

 which the firm structures can move on one another without resistance and yet securely 

 owing to the fact that they are appropriately attached to each other by strong ligaments. 

 If, then, we wish to study the skeleton, we should not confine our attention to the 

 bones, but should also consider the cartilages, ligaments, and joints that are concerned 

 in maintaining the form of the body and in enabling it to move about. 



Cartilages * are tough, but elastic and compressible to a considerable extent. In the adult 

 skeleton they are found completing the skeleton of the thorax (costal cartilages), holding bones 

 firmly together (as in the vertebral column), or filling up intervals between bones (as in certain 

 parts of the skull), coating the articular surfaces of bones (articular cartilages), or interposed between 

 two articular surfaces (inter-articular cartilages). Cartilage occurring in the body is in general of 

 the hyaline variety when covering articular surfaces of bone, but has the structure of one of the 

 varieties of fibro-cartilage in other situations, save when it is taking the place of a bone in the 

 skeleton. 



Articulations can, as a whole, be divided into synarthrodial or immovable and diarthrodial or 

 movable. Diarthrodial joints possess a synovial cavity to permit of easy movement, and this 

 cavity may be wholly or partly divided by an inter-articular cartilage or meniscus into two parts. 

 Synarthrodial joints are firmly fixed by interlocking of the bones concerned or by interposition of a 

 thin but strong layer of fibro-cartilage over a large area on each of the bones. A subdivision of this 

 class, where a certain very small amount of motion is permitted between the bones owing to the 

 intervention of a thicker pad of fibro-cartilage, is usually termed an amphiarthrosis. 



Ligaments are bands of fibrous tissue that pass over a joint to connect the bones ; naturally 

 they are best developed over diarthrodial joints, where the articulating bones have no connecting 

 medium between them, but depend on outside agents for security. It is evident that, if the liga- 

 ments are not to be a hindrance to free movement, they must be so disposed with regard to the 

 joint surfaces, and these must be so shaped with reference to the ligamentous attachments, that 

 any given ligament will either be tense and effective at one part of the movement or will remain 

 tense throughout it ; in the latter case the movement of the articulation can only occur in one 



* For detailed histology and for accounts of varieties of tissues consult special works on histology. 

 F.A. i 



