AND PHYSIOLOGY. 



is required, is not so easily explained, but it is evident that 

 one bone could not perform their function, nor the prolonga- 

 tion of the radius and ulna to the metacarpus. Several bones 

 are required in order to give easy and graceful motion to the 

 wrist, as well as strength. One bone could not answer the 

 purpose, since the very many offices, which the hand has to 

 perform, could not be effected, unless the wrist bones were 

 very strongly bound together, and flexible to a certain extent. 

 The arrangement of the bones in two rows allows a little 

 movement of the hand upon the wrist. 



175. Function of Metacarpus — The metacarpus of five 

 long bones gives support to the fingers. They are long rather 

 than short bones, in order to give slenderness to the hand, 

 and also to afford a solid surface for the fingers to meet in 

 the act of prehension. 



176. Need of three Phalanges to the Fingers, and two 

 Phalanges to the Thumb. — The phalanges of each finger are 

 three in number, whilst those of the thumb are but two. 

 The obvious reason of this is to give greater firmness to the 

 thumb, and flexibility to the fingers. The hand in man dif- 

 fers from the anterior extremity of all other animals in the 

 power of perfectly opposing the thumb to each of the fingers, 

 which of course gives him a great superiority in all delicate 

 manipulations, and especially in grasping minute objects. 

 And it is easy to see that a third phalanx in the thumb would 

 not only diminish the firmness of this member, but would 

 render the hand an awkward and clumsy organ, instead of an 

 instrument beautifully and perfectly adapted to the multi- 

 farious offices which it has to perform. 



177. The great Length of the lower Extremities. Pe- 

 culiarities of the Femur. — The value of the great length in 

 the lower extremities, is manifest as a means of rapid pro- 



Wby would not one bone be sufficient? 1T5. The use of the metacarpus. 1T6. Why 

 are there but two phalanges in the thumb and three in each finger? What would be 

 the effect of a third phalanx in the thumb ? 177. Why are the lower extremities pro- 

 portionally longer than the upper ? 



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