many vegetable feeding animals it is very long,
and even in the orang-utan it is of considerable length and convoluted.
So, man possesses rudimentary bones of a tail concealed beneath the
skin, and, in some rare cases, this forms a minute external tail.

The variability of every part of man's structure is very great, and many
of these variations tend to approximate towards the structure of other
animals. The courses of the arteries are eminently variable, so that for
surgical purposes it has been necessary to determine the probable
proportion of each variation. The muscles are so variable that in fifty
cases the muscles of the foot were found to be not strictly alike in any
two, and in some the deviations were considerable; while in thirty-six
subjects Mr. J. Wood observed no fewer than 558 muscular variations. The
same author states that in a single male subject there were no fewer
than seven muscular variations, all of which plainly represented muscles
proper to various kinds of apes. The muscles of the hands and
arms--parts which are so eminently characteristic of man--are extremely
liable to vary, so as to resemble the corresponding muscles of the lower
animals. That such variations are due to reversion to a former state of
existence Mr. Darwin thinks highly probable, and he adds: "It is quite
incredible that a man should, through mere accident, abnormally resemble
certain apes in no less than seven of his muscles, if there had been no
genetic connection between them. On the other hand, if man is descended
from some ape-like creature, no valid reason can be assigned why certain
muscles should not suddenly reappear after an interval of many thousand
generations, in the same manner as, with horses, asses, and mules, dark
coloured stripes suddenly reappear on the legs and shoulders, after an
interval of hundreds, or more probably of thousands of
generations."[218]

_The Embryonic Development of Man and other Mammalia._

The progressive development of any vertebrate from the ovum or minute
embryonic egg affords one of the most marvellous chapters in Natural
History. We see the contents of the ovum undergoing numerous definite
changes, its interior dividing and subdividing till it consists of a
mass of cells, then a groove appears marking out the median line or
vertebral column of the future animal, and thereafter are slowly
developed the various essential organs of the body. After describing in
some detail what tak