STRUCTURE OF THE HUMAN BODY 31 



by five elongated bones, which support the palm, and from their 

 shape are classed with the long bones. Fourteen small phalanges 

 of similar shape complete the skeleton of the hand, each finger 

 possessing three, while the thumb has only two. Each end- 

 phalanx is broadened out and roughened at its tip to afford^ a 

 support to a nail. 



Two further points of interest deserve mention in regard to 

 the hand. One is the unequal lengths of the digits (or fingers), 

 a device which renders them much more efficient in delicate 

 manipulations, enabling their tips to be brought together with 

 great ease. The other point is the opposability of the thumb, 

 i.e. it can be bent over so as to directly oppose any one of the 

 fingers. How important a matter this is may be realized by 

 trying to pick up a small object, say a pin, by means of the 

 fingers alone. The arrangement is rendered possible by the 

 peculiar nature of the joint between the base of the thumb and 

 the wrist. The opposing surfaces are here saddle-shaped, allow- 

 ing a much larger range of movement than any other combination 

 of curves. The same kind of jointing is found in a bird's neck, 

 which is well known to be exceedingly flexible. 



2. The Leg. — Here we find in the first place a hip-girdle, 

 comparable to the shoulder-girdle of the upper limb. But the 

 necessity for supporting the very considerable weight of the 

 body has in this case brought about an intimate union with the 

 skeleton of the trunk, and the two girdles are firmly united with 

 one another and with the sacrum to form the basin-like pelvis 

 mentioned above (see p. 27). Each girdle is constituted by an 

 irregular hip-bone, consisting of three elements fused together, 

 and corresponding to what in many animals are clearly to be 

 distinguished as three separate bones. The pelvis is arched so 

 as the better to support the weight of the body transmitted to it, 

 and thence to the thigh-bones, by means of the sacrum, which 

 may be compared to the keystone of the arch. A further use 

 of the pelvis is to protect certain delicate internal organs placed 

 within its cavity. 



On the outer side of each hip-bone is a deep cup for re- 

 ceiving the globular upper end of the large femur, or thigh-bone, 

 which is comparable to the humerus in the upper arm. The joint 

 at the thigh, like that at the shoulder, is of the ball-and-socket 

 kind, but here greater firmness is necessary, and consequently less 



