286 APPENDIX. 



concealed in the flanks, with a corresponding elongation of the heel, 

 the toe only touching the ground. 



Laws of Comparative Anatomy. The foregoing remarks upon 

 homologies and analogies prepare for a deduction of some of those 

 great laws of coexistence which lie at the foundation of comparative 

 anatomy. 



1. Since the extremities by means of which the animal procures 

 its food must always bear a certain relation to the teeth which mas- 

 ticate and fit it for the stomach, the former decide the animal's 

 external structure, and the latter its internal organization. 



2. The position and size of the processes of different bones deter- 

 mine the direction and force of the muscles by which they are worked. 



3. The character of the muscles determines the structure of the 

 nerves which call them into action, and of the brain in which the 

 nerves originate. 



4. The nervous system determines the degree of intelligence. 



The structure of an animal, its natural habit and mode of life, 

 can be deduced from the bones of the extremities, and even from 

 the ends only of any one of them. For instance, the shape of a 

 single finger-bone indicates the necessary form of the one with which 

 it articulates ; this latter its fellow, and so on through the series 

 including the metacarpal, carpal, radius and ulna, humerus, scapula 

 and clavicle. The result of this investigation suggests at once to a 

 comparative anatomist the structure of the teeth, whether herbiv- 

 orous or carnivorous, and thus enables him to decipher the entire 

 character of the animal. Any bone in the series answers equally 

 well for a starting-point, and the skill of the investigator is shown 

 in the readiness with which he reconstructs the whole bony fabric 

 from the extremity furnished. Thus Cuvier, from single bones found 

 in the gypsum near Paris, drew the entire outline of fossil genera of 

 mammals ; and Agassiz, from isolated scales, restored the whole fish. 

 (See "Geology," pp. 182 and 203.) 



