7Q DOMESTIC PIGS. Chap. III. 



tliat rich and abundant food, given during youth, tends by 

 some direct action to make the head broader and shorter ; 

 and that poor food works a contrary result. He lays much 

 stress on the fact that all wild and semi-domesticated pigs, 

 in ploughing up the ground with their muzzles, have, 

 whilst young, to exert the powerful muscles fixed to the 

 hinder part of the head. In highly cultivated races this 

 habit is no longer followed, and consequently the back of 

 the skull becomes modified in shape, entailing other changes 

 in other parts. There can hardly be a doubt that so great 

 a change in habits would affect the skull ; but it seems 

 rather doubtful how far this will account for the greatly 

 reduced length of the skull and for its concave front. It is 

 well known (Nathusius himself advancing many cases, 

 s. 104) that there is a strong tendency in many domestic 

 animals — in bull- and pug-dogs, in the niata cattle, in 

 sheep, in Polish fowls, short-faced tumbler pigeons, and in 

 one variety of the carp — for the bones of the face to become 

 greatly shortened. In the case of the dog, as H. Mtiller has 

 shown, this seems caused by an abnormal state of the pri- 

 mordial cartilage. We may, however, readily admit that 

 abundant and rich food supplied during many generations 

 would give an inherited tendency to increased size of body, 

 and that, from disuse, the limbs would become finer and 

 shorter. 18 We shall in a future chapter see also that the 

 skull and limbs are apparently in some manner correlated, 

 so that any change in the one tends to affect the other. 



Nathusius has remarked, and the observation is an in- 

 teresting one, that the peculiar form of the skull and body 

 in the most highly cultivated races is not characteristic of 

 any one race, but is common to all when improved up to the 

 same standard. Thus the large-bodied, long-eared, English 

 breeds with a convex back, and the small-bodied, short-eared, 

 Chinese breeds with a concave back, when bred to the same 

 state of perfection, nearly resemble each other in the form 

 of the head and body. This result, it appears, is partly due 

 to similar causes of change acting on the several races, and 



18 Nathusius, ' Die Racen des Schweines,' s. 71. 



