The Descent of Man

y Prof. Turner, has been expressly described
by Theile as a rudimentary repetition of the
extensor of the tail, a muscle which is so largely
developed in many mammals.
The spinal cord in man extends only as far
downwards as the last dorsal or first lumbar
vertebra; but a thread-like structure (the filum
terminale) runs down the axis of the sacral part
of the spinal canal, and even along the back of
the coccygeal bones. The upper part of this filament,
as Prof. Turner informs me, is undoubtedly
homologous with the spinal cord;
but the lower part apparently consists merely
of the pia mater, or vascular investing membrane.
Even in this case the os coccyx may be
said to possess a vestige of so important a
structure as the spinal cord, though no longer
enclosed within a bony canal. The following
fact, for which I am also indebted to Prof.
Turner, shews how closely the os coccyx corresponds
with the true tail in the lower animals: