i8 



EVOLUTION AND DISEASE. 



and found the muscular coat increased in thickness. 

 This simple experiment has been varied by other 

 observers with similar results. 



The large breast muscles (pectorals) of birds associated 

 with and varying according to the expanse of wing, 

 furnish a good example of the relation of increased size 

 with augmented use ; these may be compared with the 



FlG. 9. A medium longitudinal section through the third 

 finger of a horse, and man. M, metacarpal bone ; i, 2, 3, 

 phalanges. The ossicle, N, situated at the junction of the 

 second and third phalanges is the navicular. 



powerful leg muscle of the frog (known as the gastro- 

 cnemius) so important in the act of swimming, and the 

 large muscles of the human buttock, useful in helping 

 man to maintain the erect position. These are striking 

 instances of the inherited effects of increased use of a 

 part. 



