312 
OLOF SCHWARTZKOPFF. 
Besides the nutrition influence, a strong or weak muscular 
action plays an important part in the production of form The 
pulling and pressure of muscles extensively used for certain 
purposes, especially those of the head and neck, will give the 
head a characteristic shape. Pigs which are prevented from 
rooting will acquire a short, high and rounded head, while 
those which are forced to root to secure a portion of their 
food will develop a long and slender form of head. If we 
force both experiments to the greatest degree possible, we 
shall produce those extremes which distinguish the wild pig 
from our improved races. That this is true is proven by the 
fact that when our domestic hogs are returned to absolute 
liberty, it will require but a few generations to reproduce the 
original skull of the wild pig. And, vice versa , we have called 
into existence from the primitive hog all those different rep¬ 
resentative types of our day, by careful and continued selec¬ 
tion, gradual assortment, and particular attention to the de¬ 
sired qualities of form, size, etc. The striking difference 
between the skull of a primitive hog and a modern one is seen 
in the following illustrations : 4 
Fig. V. 
Skull of a full grown primitive Texas Boar, 
(Original). 
