alternate contraction and relaxation of the artery
after the ligature of the aorta, is certainly most
powerful; indeed it scarcely admits of a remaining *
doubt of the structure and function of the arteries.
Still it is important that this possible doubt should
be removed. This is finally effected, I think, by
the fact which I am about to detail.
3. Description of an Artery in the Frog and
Toad, which pulsates independently of the Heart.
Whatever presumption there might be in the
arguments and facts which have been laid before
the reader, for the contractile influence of the
arteries, we still wanted a direct proof of this
process, until I discovered the interesting fact of
an artery in the frog and toad, which pulsates
distinctly, for a considerable time after the removal
of the heart.
The artery to which I allude, is a branch
from each of the arteries which in the frog and
toad, after separating at a short distance from
the heart, rejoin and form the aorta. Pursuing
its course backwards and downwards, it passes
under the transverse process of the third vertebra.
It is here bound down. It is also very
tortuous. When the viscera are removed, two
pulsating points are distinctly seen at this part.
On a minute examination, these pulsating points
are found to be portions of cellular and muscular
textures, above and below the transverse
process just mentioned, moved by the contraction
of a subjacent artery.
On removing these textures carefully, and on
removing the skin from the back of the animal,
the part along which the artery passes on emerging
from beneath the transverse process, is
sufficiently thin and transparent to admit of its
being placed under the microscope. The artery
is then plainly seen to pulsate, becoming straighter
and paler at each contraction. The adjacent.
textures are moved, at the same time, and the
blood is frequently seen to oscillate in a branch
of the same artery situated very near it.
The course of this artery is depicted in Plate
IX. The transverse process of the third vertebra,
is larger and more prominent than the rest.
Just above it, is seen a pulsating point. Immediately
below it, is seen another pulsating point;
and in this latter part, the course of the artery, its
straightened form and paler colour at each con