a scarcely visible stump, containing only three or four vertebrae. In
some kinds of baboons there are twenty-five, whilst in the mandrill
there are ten very small stunted caudal vertebrae, or, according to
Cuvier (90. Mr. St. George Mivart, Proc. Zoolog. Soc. 1865, pp. 562,
583. Dr. J.E. Gray, Cat. Brit. Mus.: Skeletons. Owen, Anatomy of
Vertebrates, vol. ii. p. 517. Isidore Geoffroy, Hist. Nat. Gen. tom.
ii. p. 244.), sometimes only five. The tail, whether it be long or
short, almost always tapers towards the end; and this, I presume,
results from the atrophy of the terminal muscles, together with their
arteries and nerves, through disuse, leading to the atrophy of the
terminal bones. But no explanation can at present be given of the great
diversity which often occurs in its length. Here, however, we are more
specially concerned with the complete external disappearance of the
tail. Professor Broca has recently shewn (91. Revue d Anthropologie,
1872; La Constitution des vertebres caudales. ) that the tail in all
quadrupeds consists of two portions, generally separated abruptly from
each other; the basal portion consists of vertebrae, more or less
perfectly channelled and furnished with apophyses like ordinary
vertebrae; whereas those of the terminal portion are not channelled,
are almost smooth, and scarcely resemble true vertebrae. A tail, though
not externally visible, is really present in man and the
anthropomorphous apes, and is constructed on exactly the same pattern
in both. In the terminal portion the vertebrae, constituting the os
coccyx, are quite rudimentary, being much reduced in size and number.
In the basal portion, the vertebrae are likewise few, are united firmly
together, and are arrested in development; but they have been rendered
much broader and flatter than the corresponding vertebrae in the tails
of other animals: they constitute what Broca calls the accessory sacral
vertebrae. These are of functional importance by supporting certain
internal parts and in other ways; and their modification is directly
connected with the erect or semi-erect attitude of man and the
anthropomorphous apes. This conclusion is the more trustworthy, as
Broca formerly held a different view, which he has now abandoned. The
modification, therefore, of the basal caudal vertebrae in man and the
higher apes may have been effected, directly or indirectly, through
natural selection.
But what are we to say about the rudimentary and variable vertebrae of
the terminal portion of the tail, forming the os coccyx? A notion which
has often been, and will no doubt again be ridiculed, namely, that
69