_Comparative Anatomy._--The wrist joint of the lower Mammals allows less lateral movement than does that of Man, while the lower end of the ulna is better developed and is received into a cup-shaped socket formed by the cuneiform and pisiform bones. At the same time, unless there is pretty free pronation and supination, the triangular fibro-cartilage is only represented by an interosseous ligament, which may be continuous above with the interosseous membrane between the radius and ulna, and suggests the possibility that the fibro-cartilage is largely a derivative of this membrane. In most Mammals the wrist is divided into two lateral parts, as it is in the human foetus, but free pronation and supination seem to cause the disappearance of the septum. _Joints of the Lower Extremity._ The _sacro-innominate articulation_ consists of the _sacro-iliac joint_ and the _sacro-sciatic ligaments_. The former is one of the amphiarthroses or half-joints by which the sacrum is bound to the ilium. The mechanism of the human sacrum is that of a suspension bridge slung between the two pillars or ilia by the very strong _posterior sacro-iliac_ ligaments which represent the chains. The axis of the joint passes through the second sacral vertebra, but the sacrum is so nearly horizontal that the weight of the body, which is transmitted to the first sacral vertebra, tends to tilt that part down. This tendency is corrected by the great and small _sacro-sciatic ligaments_, which fasten the lower part of the sacrum to the tuberosity and spine of the ischium respectively, so that, although the sacrum is a suspension bridge when looked at from behind, it is a lever of the first kind when seen from the side or in sagittal section. The _pubic symphysis_ is the union between the two pubic bones. It has all the characteristics of a symphysis, already described, and may have a small median cavity. [Illustration: (From David Hepburn, Cunningham's _Text-book of Anatomy_.) FIG. 6.--Dissection of the Hip Joint from the front.]