of left foot, showing muscles, blood vessels and
other internal organs.]
Plate 68, Figure 2

CONCLUDING COMMENTARY.
ON THE FORM AND DISTRIBUTION OF THE VASCULAR SYSTEM AS A WHOLE.
ANOMALIES.--RAMIFICATION.--ANASTOMOSIS.

I.--The heart, in all stages of its development, is to the vascular
system what the point of a circle is to the circumference--namely, at
once the beginning and the end. The heart, occupying, it may be said,
the centre of the thorax, circulates the blood in the same way, by
similar channels, to an equal extent, in equal pace, and at the same
period of time, through both sides of the body. In its adult normal
condition, the heart presents itself as a double or symmetrical organ.
The two hearts, though united and appearing single, are nevertheless, as
to their respective cavities, absolutely distinct. Each heart consists
again of two compartments--an auricle and a ventricle. The two auricles
are similar in structure and form. The two ventricles are similar in the
same respects. A septum divides the two auricles, and another--the two
ventricles. Between the right auricle and ventricle, forming the right
heart, there exists a valvular apparatus (tricuspid), by which these two
compartments communicate; and a similar valve (bicuspid) admits of
communication between the left auricle and ventricle. The two hearts
being distinct, and the main vessels arising from each respectively
being distinct likewise, it follows that the capillary peripheries of
these vessels form the only channels through which the blood issuing
from one heart can enter the other.

II.--As the aorta of the left heart ramifies throughout all parts of the
body, and as the countless ramifications of this vessel terminate in an
equal number of ramifications of the principal veins of the right heart,
it will appear that between the systemic vessels of the two hearts
respectively, the capillary anastomotic circulation reigns universal.

III.--The body generally is marked by the median line, from the vertex
to the perinaeum, into corresponding halves. All parts excepting the
main bloodvessels in the neighbourhood of the heart are naturally
divisible by this line into equals. The vessels of each heart, in being
distributed to both sides of the body alike, cross each other at the
median line, and hence they are inseparable according to this line,
unless by section. If the vessels proper to each heart, right and left,
ramified alone withi