362 CuntribuUons to the 



state of permanent pronation, is a good example of the 

 adherence to a general plan, with the addition of a part 

 for special use, or, from the opposite point of view, of the 

 total disappearance of a part when no longer needed. I 

 found the same structure in a young sheep, but have never- 

 noticed it in the Carnivora. The flexors and extensors of 

 the wrist do not differ from those in man, except that the 

 Flexor ulnaris is larger, as also the pisiform bone to which 

 it is attached. In the Chimpanzee, as in man, the Flexor 

 carpi ulnaris is more powerful than the Flexor carpi radi- 

 alis ; tne former is clearly the one which we use in the 

 more forcible movements of the hand at the wrist, in stick- 

 ing a blow, or in reaping with a sickle ; it is also full as 

 good a supinator as the Supinator longus, and in nearly 

 all actions requiring forcible supination, as turning a han- 

 dle, &c., the hand is flexed to the ulnar side at the same 

 time. 



It is a general rule, that two contiguous segments of a 

 limb are flexed in opposite directions, as is well shown in 

 the human lower extremity, where thigh, leg, foot, and 

 toes all bend thus contrary to each other, the flexor mus- 

 cles of one segment lying, of course, on the same side of 

 the limb with the extensors of the segment next below. 

 Tliis holds good in the leg and upper arm of most ani- 

 mals as well as man^ but in nearly all, the hand and fin- 

 gers, and, if the hand is supinated as in man and Quadru- 

 mana, the forearm also, appear to be flexed or extended in 

 the same direction, so that two, or even three groups of 

 muscles, which by their contraction shorten the arm, lie 

 all upon the same side of the limb, though attached to 

 three contiguous segments, — forearm, hand, and fingers. 

 But to carry out the idea of " antero-posterior symme- 

 try " or antagonism between the corresponding segments 

 of the fore and hind limbs, the supinated hand must be 

 placed palm downward, with the fingers pointing back- 

 ward, when of course the muscles now called extensors of 



