Human skeleton, structure and joints. Part one. (1951)

this framework together with the muscles which move the bones gives the body form and shape the skeleton is made up of a central or axial portion a left appendicular portion the central or actual part of the skeleton of the bones of the head neck these include the skull the vertebral column which supports the skull and the ribs and sternum the ribs and sternum with part of the vertebral column form the chest or thorax the appendicular part of the skeleton is made up of the paired bones of the limbs in the lower limbs to strong hip bones support the trunk and in turn are supported by the bones of the thighs legs and feet in the upper limbs the lighter shoulder girdles join the arms to the trunk the place at which two or more bones meet is called a joint for articulation for instance two bones meet to form the shoulder joint and three bones meet to form the elbow joint a shoulder and elbow joints are movable but some joints are immobile such as those found in the skull the skull forms a protective case for the brain and its bones have saw-like edges which fit tightly into each other these a movable joints in the skull are called sutures the body also has joints which are slightly movable such as those found in the vertebral column or spine because the vertebral column has such a large number of these slightly movable joints the trunk can be moved quite freely forwards backwards and from side to side at the top of the column freely movable joints allow a greater range of movement for the head such as looking over the shoulder the vertebral joints are slightly movable because they have pads of fibrocartilage joining the bones these pads of fibrocartilage can be compressed in front at the back and at the sides thus allowing movement of the column the legs and arms have the greatest number of freely movable joints in this action the shoulder elbow forearm wrist and finger joints are all being brought into play let us look at one type of movable joint the elbow joint in all movable joints the number and direction of the movements depend on the shape of the articulating surfaces of the bones at the elbow one of the forearm bones the honor has a Halfmoon shaped surface this moves forwards and backwards on the pulley like surface of the humerus the radius glides with it this is a hinge joint when the movement of the joint is watched by means of x-rays the softer tissues like the muscles hardly show although the bones can clearly seen another important our movement is the turning movement in the forearm which takes place at the joints between the radius and the ulna here the movement is being seen by means of x-rays notice how the radius turns round the owner carrying the wrist with it the greatest range of our movement is found at the shoulder joint at this joint the arm can be moved quite freely the same kind of joint is found at the hip and the same movements can be made though not quite so free the leg can move forwards backwards outwards and inwards described a circle and make a turning movement the shoulder and hip joins are universal or ball and socket joints at the hip the rounded head of the femur or thighbone fits into the deep socket of the hip bone watch the head of the femur move in the socket as the thigh bone moves forwards backwards outward and inwards in a circular movement and in a turning movement in freely movable joints the articulating surfaces of the bones are covered by a thin layer of smooth cartilage this reduces friction the ends of the bones are enclosed in a protective sheath of white fibrous tissue called the capsular ligament the capsular ligament has a lining which extends along the bone to meet the edge of the cartilage this lining a synovial membrane makes a lubricating fluid which further reduces friction the capsule may be thickened in places to give extra strength joints of this kind and the other types we have seen make movement possible movement itself is brought about by muscles attached to the bones these bones form a jointed framework the skeleton round which the body is built