118 ARTIIROLOGY. 



opposite sides of the base of support, and the long neck of the femur gives an advan- 

 tageous insertion to the muscles by which the balance of the body on the thigh is prin- 

 cipally preserved (viz., the adductor and gluteal muscles), placing them more nearly at 

 right angles to the bones on which they act. The os innominatum is principally dis- 

 tinguished from the same bone in animals by the breadth of the iliac portion, which 

 gives support to the viscera and attachment to -the greatly developed gluteal muscles, 

 by the shortness and strength of the pillar of bone extending from the auricular 

 surface to the acetabulum, and by the marked nature of the angle which the pubic 

 part forms with the iliac, as it passes inwards from the acetabulum to the symphysis, 

 and thus completes the peculiarly broad pelvis. The strong and expanded sacrum 

 supports the spinal column, while the short coccyx is bent forwards and aids in 

 forming the floor of the pelvic cavity. The spinal column, by its pyramidal form, 

 is fitted to sustain the weight which bears down upon its lower part, and by means 

 of its different curvatures gives elasticity and strength, and allows considerable 

 range of motion to the trunk without removal of the centre of gravity from within 

 its base. The thorax is so formed as to bring the weight of its contents very much 

 over and to the sides of the bodies of the vertebrae rather than in front. Thus, 

 the thorax is broad from side to side, and compressed from before backwards ; the 

 transverse processes and proximal parts of the ribs are inclined backwards, so as 

 to enlarge the chest behind the transverse plane of the bodies of the vertebrae, 

 and the axis of the cavity is directed upwards and backwards, so that its contents 

 may thus be supported on the column in the erect posture. The upper limbs are 

 also thrown outwards and backwards by the long clavicles which support them 

 and form the fulcra of their free movements. The blades of the scapulae are 

 thus made to lie more nearly in one transverse plane, with the glenoid fossae looking 

 outwards, a position manifestly unsuited to the support of the weight of the body on 

 the limb. In those animals which habitually use their fore limbs for support, the 

 glenoid fossae look downwards, and rest on the humeri ; but if the human body be 

 placed so as to be rested on the hands, the glenoid cavity lies on the inside of the 

 head of the humerus, and the scapula is supported upon the humerus by the acromion 

 process. While stability and strength have been provided in the lower limb, mobility* 

 and lightness have been secured in the upper. This is apparent on comparison of 

 the shoulder, elbow, and wrist, with the hip, knee, and ankle. In the hand also, 

 the movable phalanges are as long as the carpal and metacarpal bones taken together, 

 whereas in the foot they are not a third of the length of the tarsal and metatarsal 

 bones. The skull of man differs from that of animals in being nearly balanced on 

 the vertebral column, the condyles of the occipital bone being brought forwards 

 towards the middle of the base, by the comparative shortness of that part of the skull 

 which lies in front of the foramen magnum, and the projection backwards of that 

 which lies behind it. In animals the skull hangs forwards, as it were, from the 

 extremity of the column, and is sustained by an elastic substance (ligamentum 

 nuchae), which is attached on, the one hand to the spinous processes of the vertebrae, 

 and on the other to the occipital protuberance. 



SECTION II. ARTHROLOGY. 



MODES OP ARTICULATION. 



THE name of articulation, synonymous with joint, is given in descriptive 

 anatomy to the connection subsisting in the recent skeleton between any of 

 its denser component parts, whether bones or cartilages. In all instances, 

 excepting the bones of the head, which are so closely set together in the 

 sutures as to have no more than the fibrous periosteum between them, 

 some softer intervening substance lies between the bones, uniting them 

 together, or clothing the surfaces which are opposed ; but the manner 

 in which the several pieces of the skeleton are thus connected, or the 

 modes of articulation, vary to a great degree both in the form and nature 

 of the uniting substances, and in the extent of motion which they allow 



