riginal observer. It
is remarkable that Aristotle should have overlooked the presence of the
valves of the heart, the structure and functions of which were fully
investigated within thirty years of his death by the anatomists of the
Alexandrian school. This is the more remarkable, as he calls attention
here, and in the "History of Animals," to the sinews or tendons
({neura}) with which, he says, the heart is supplied, and by which he
probably meant chiefly the _chordae tendineae_. The "bone in the heart" of
which he speaks was probably the cruciform ossification which is
normally found in the ox and the stag below the origin of the aorta. It
is found in the horse only in advanced age, or under abnormal
conditions. The statement that the heart contains no more than three
chambers has always been considered as a very gross blunder on the part
of Aristotle. Even Cuvier, who generally lavishes upon the philosopher
the most extravagant praise, sneers at this. Professor Huxley,[9]
however, has shown, by a comparison of several passages from the
"History of Animals," that what we now call the right auricle was
regarded by the author as a venous sinus, as being a part not of the
heart, but of the great vein (_i.e._ the superior and the inferior _venae
cavae_).

Aristotle speaks of the _lung_ as a single organ, sub-divided, but
having a common outlet--the trachea. Elsewhere[10] he says, "Canals from
the heart pass to the lung and divide in the same fashion as the
windpipe does, closely accompanying those from the windpipe through the
whole lung." His theory of respiration, as explained in his treatise on
the subject, is that it tempers the excessive heat produced in the
heart. The lung is compared to a pair of bellows. When the lung is
expanded, air rushes in; when it is contracted, the air is expelled. The
heat from the heart causes the lung to expand--cold air rushes in, the
heat is reduced, the lung collapses, and the air is expelled. The cold
air drawn into the lung reaches the bronchial tubes, and as the vessels
containing hot blood run alongside these tubes, the air cools it and
carries off its superfluous heat. Some of the air which enters the lung
gets from the bronchial tubes into the blood-vessels by transudation,
for there is no direct communication between them; and this air,
penetrating the body, rapidly cools the blood throughout the vessels.
But Aristotle did not consider the "pneuma," which thus reached the
inte