CirAP. IV. EFFECTS OF USE AND DISUSE. 129 



size, — I conclude, notwithstanding the remarkable differences in 

 capacity in the skulls of the small P. Santo rabbits, and likewise 

 in the large lop-eared kinds, that in all long-domesticated rabbits 

 the brain has either by no means increased in due proportion 

 with the increased length of the head and increased size of the 

 body, or that it has actually decreased in size, relatively to what 

 would have occurred had these animals lived in a state of nature. 

 When we remember that rabbits, from having been domesticated 

 and closely confined during many generations, cannot have 

 exerted their intellect, instincts, senses, and voluntary move- 

 ments, either in escaping from various dangers or in searching 

 for food, we may conclude that their brains will have been feebly 

 exercised, and consequently have suffered in development. We 

 thus see that the most important and complicated organ in 

 the whole organisation is subject to the law of decrease in 

 size from disuse. 



Finally, let us sum up the more important modifications 

 which domestic rabbits have undergone, together with their 

 causes as far as we can obscurely see them. By the supply of 

 abundant and nutritious food, together with little exercise, and 

 by the continued selection of the heaviest individuals, the weight 

 of the larger breeds has been more than doubled. The bones of 

 the limbs have increased in weight (but the hind legs less than 

 the front legs), in due proportion with the increased weight of 

 body ; but in length they have not increased in due proportion, 

 and this may have been caused by the want of proper exercise. 

 With the increased size of the body the third cervical vertebra 

 has assumed characters proper to the fourth cervical ; and the 

 eighth and ninth dorsal vertebras have similarly assumed cha- 

 racters proper to the tenth and posterior vertebras. The skull 

 m the larger breeds has increased in length, but not in due pro- 

 portion with the increased length of body ; the brain has not 

 duly increased in dimensions, or has even actually decreased, and 

 consequently the bony case for the brain has remained narrow, 

 and by correlation has affected the bones of the face and the 

 entire length of the skull. The skull has thus acquired its 

 characteristic narrowness. From unknown causes the supra- 

 orbital processes of the frontal bones and the free end of the 

 malar bones have increased in breadth ; and in the larger breeds 



VOL. I. 



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