^HANDBOOK OF ANATOMY 



terms proximal and distal are used to indicate positions near 

 to or distant from the trunk. 



The body consists of a bony framework, the component parts 

 of which are jointed together, the joints being the fulcrums 

 of the levers formed by the muscles. As well as the skeletal 

 and muscular systems, the circulatory, respiratory, digestive, 

 and nervous systems also have to be studied. 



The Skeletal System. The bones are classed as long, short, 

 flat, or irregular, according to their shape. They are all laid 

 down in cartilage in the embryo, and become ossified at different 

 stages. Various centres of ossification are laid down in different 

 parts of the bone, so that each part can continue growing 

 until the adult size is reached, by which time the different 

 centres of ossification have coalesced and the bone is completely 

 ossified. A sesamoid bone is one that is developed in a tendon 

 passing over a joint where there is a great deal of friction. 



Joints are formed by the ends of two bones in apposition to 

 one another. Fibrous bands, called " ligaments," hold them to- 

 gether, and these generally join one another so as to form a 

 complete capsule round the joint. The opposed ends of the 

 bones are covered with cartilage of a particularly tough kind 

 to prevent wear by friction. In some cases where the joint has 

 constant work e.g., the knee-joint an extra piece of cartilage 

 in the form of a disc is found between the bones. The whole 

 structure is lined by synovial membrane a thin membrane 

 which secretes a fluid for the purpose of lubrication. 



The skeleton consists of a vertebral column which supports the 

 trunk, and on the top of which is the head, on the freely 

 movable cervical vertebrae ; the lower end of the vertebral 

 column is firmly welded together to support the weight of the 

 body. The upper half of the body the thorax is protected 

 by a bony framework formed by the ribs, which are elastic 

 and freely movable, to give free play to the lungs. The lower 

 half of the trunk, the abdomen, has only partial bony pro- 

 tection and a strong muscular wall composed of three layers 

 of muscles with the fibres arranged in different directions, so 

 that they can exert strong contractile force. 



The limbs are similiar in structure as to the number and 



