THE HAND. 31 



of tliis range, as well as the metacarpal bones, present the 

 concavity of an arch towards the object pressed on, and have 

 the ligaments which support them in that position thrown 

 into a state of tension, which, being recovered from as soon 

 as the pressure is removed, gives elasticity to the movements 

 of the limb. The utility of the hand depends in great 

 measure on the opposability of the thumb to the other digits, 

 and this results from freedom of movement between the 

 trapezium and first metacarpal bone, and from the number 

 of muscles attached to the thumb. - 



15. The fifth or lowest lumbar vertebra rests on the broad 

 upper end of a curved wedge, the sacrum, which consists of 

 five other vertebra fused together in one bone; and at the 

 lower and narrow end of this bone are four more of a rudi- 

 mentary description, corresponding with the caudal vertebrae 

 or bones of the tail in other animals, but usually named by 

 the human anatomist, collectively, the coccyx. 



On its sides, in the upper two-thirds of its extent, the 

 sacrum, is closely united to the two pelvic or innominate 

 bones, which, together with it, enclose a basin or cavity, 

 called the pelvis. Examined in early life, each innominate 

 bone is seen to consist of three parts, which meet at the 

 articular cup, called the acetabulum, for the head of the 

 thigh bone. The expanded upper part is called the ilium, 

 the lower part is called the ischium, while t the part which 

 meets with the opposite bone in the middle line is the os 

 pubis, and the union is called the symphysis pubis. The 

 expanded ilium obviously corresponds with the shoulder- 

 blade in the upper limb, and the pair of innominate 

 bones with the shoulder-girdle, notwithstanding that the 

 shoulder-girdle is but little connected with the trunk, while 

 the innominate bones take an important part in bounding 

 the visceral cavity. 



From the upper end of the sacrum a prominent ring of 

 the innominate bone can be followed round to the symphysis 

 pubis, constituting the brim of the true pelvis as distin- 

 guished from the part of the abdomen between the blades oi 

 the iliac bones. In the erect posture of the body this ring 

 lies at an angle of 60 with the horizontal, so that the 

 sacrum, presses downwards on it. But the sacrum is so 



