Schaaffhausen accounts for this difference between the races by "the
posterior dental portion of the jaw being always shortened" in those that
are civilised (44. 'On the Primitive Form of the Skull,' Eng. translat.,
in 'Anthropological Review,' Oct. 1868, p. 426), and this shortening may, I
presume, be attributed to civilised men habitually feeding on soft, cooked
food, and thus using their jaws less. I am informed by Mr. Brace that it
is becoming quite a common practice in the United States to remove some of
the molar teeth of children, as the jaw does not grow large enough for the
perfect development of the normal number. (45. Prof. Montegazza writes to
me from Florence, that he has lately been studying the last molar teeth in
the different races of man, and has come to the same conclusion as that
given in my text, viz., that in the higher or civilised races they are on
the road towards atrophy or elimination.)

With respect to the alimentary canal, I have met with an account of only a
single rudiment, namely the vermiform appendage of the caecum. The caecum
is a branch or diverticulum of the intestine, ending in a cul-de-sac, and
is extremely long in many of the lower vegetable-feeding mammals. In the
marsupial koala it is actually more than thrice as long as the whole body.
(46. Owen, 'Anatomy of Vertebrates,' vol. iii. pp. 416, 434, 441.) It is
sometimes produced into a long gradually-tapering point, and is sometimes
constricted in parts. It appears as if, in consequence of changed diet or
habits, the caecum had become much shortened in various animals, the
vermiform appendage being left as a rudiment of the shortened part. That
this appendage is a rudiment, we may infer from its small size, and from
the evidence which Prof. Canestrini (47. 'Annuario della Soc. d. Nat.'
Modena, 1867, p. 94.) has collected of its variability in man. It is
occasionally quite absent, or again is largely developed. The passage is
sometimes completely closed for half or two-thirds of its length, with the
terminal part consisting of a flattened solid expansion. In the orang this