266 MR. MAY HEW ON PHYSIOLOGY OF THE HEART. 
facts have long been known to anatomists and physiologists. 
For example, in Dr. John Reid’s article on the Heart in the 
c Cyclopaedia of Anatomy and Physiology/ p. 28, col. 2d 
(1838), the following passage occurs: “The terminations of 
the cavae and pulmonary veins are seen to contract simul- 
taneously with the fibres of the auricles ; but sometimes they 
are seen to contract previously to the auricles, into which they 
expel their blood. In cold-blooded animals, this contraction 
of the terminations of the large veins extends over a greater 
surface, and is visible in the venae hepaticae. Judging from 
the number of muscular fibres which surround the terminations 
of the pulmonary veins in the human species, we would expect 
these contractions to occur to a greater extent in these veins 
than in the cavae. These contractions in the veins must assist 
the vis a tergo , or the force with which the column of blood 
flows along the veins towards the heart, in limiting the regur- 
gitation along these during the contraction of the auricles.” 
In the course of his argument Mr. May hew asks, rather 
irrelevantly I think, how we can, “according to our present 
theory, account for the circulation being carried on in those 
instances, when the pericardium covering the ventricles has 
been changed to bone ?” I cannot see anything to hinder the 
circulation from going on quite well, as it always does in these 
cases, so long as the pericardium alone is the seat of the 
ossification. The pericardium is merely useful to fix the 
heart in its place, and to moderate its motions ; and these 
functions v. ill not be materially impaired by its partial ossi- 
fication. 
In discussing the circulation of the heart, Mr. Mayhew 
has fallen into a vulgar error. He remarks, ft the heart may 
have four cavities.” That is perfectly true. “ But it has 
only tzvo cavities oj)en at one time , since as one exgmnds the other 
closes .” Now, this is not strictly true. The heart, for a certain 
time during each pulsation, has all its cavities open. For, 
immediately after the ventricular systole, the auricles are not 
found quite full, and go on filling with the venous blood, 
part of which also passes directly on to the ventricles. — 
[Carpenter.) When the auricles then are full, and ready to 
contract, the ventricles are partially dilated. In fact. Dr. 
Carpenter also states that seven eighths of the period of one 
pulsation is occupied by the dilatation of the auricles, and only 
one eighth by their contraction. While, as to the ventricles, 
their contraction occupies one half of the period of one pulsa- 
tion, and their dilatation the other half. It is, therefore, 
obvious, that during three eighths of the time of one pulsation, 
all the four cavities will be dilated together. 
