e great breeder who had used pure Chinese pigs
assured me that the fertility of the half-breeds _inter se_ and of their
recrossed progeny was actually increased; and this is the general belief of
agriculturists. Again, the Japan pig or _S. pliciceps_ of Gray is so
distinct in appearance from all common pigs, that it stretches one's belief
to the utmost to admit that it is simply a domestic variety; yet this breed
has been found perfectly fertile with the Berkshire breed; and Mr. Eyton
informs me that he paired a half-bred brother and sister and found them
quite fertile together.

The modifications of the skull in the most highly cultivated races are
wonderful. To appreciate the amount of change, Nathusius' work, with its
excellent figures, should be studied. The whole of the exterior of the
skull in all its parts has been altered; the hinder surface, instead of
sloping backwards, is directed forwards, entailing many changes in other
parts; the front of the head is deeply concave; the orbits have a different
shape; the auditory meatus has a different direction and shape; the
incisors of the upper and lower jaws do not touch each other, and they
stand in both jaws above the plane of the molars; the canines of the upper
jaw stand in front of those of the lower jaw, and this is a remarkable
anomaly: the articular surfaces of the occipital condyles are so greatly
changed in shape, that, as Nathusius remarks (s. 133), no naturalist,
seeing this important part of the skull by itself, would suppose that it
belonged to the genus Sus. These and various other modifications, as
Nathusius observes, can hardly be considered as monstrosities, for they are
not injurious, and are strictly inherited. The whole head is much
shortened; thus, whilst in common breeds its length to that of the body is
as 1 to 6, in the "cultur-races" the proportion is as 1 to 9, and even
recently as 1 to 11.[158] The following woodcut[159] {72} of the head of a
wild boar and of a sow from a photograph of the Yorkshire Large Breed, may
aid in showing how greatly the head in a highly cultivated race has been
modified and shortened.

[Illustration: Fig. 3.--Head of Wild Boar, and of "Golden Days," a pig of
the Yorkshire Large Breed; the latter from a photograph. (Copied from
Sidney's edit. of 'The Pig,' by Youatt.)]

Nathusius has well discussed the causes of the remarkable changes in the
skull and shape of the body which the highly cultivated races have
under