leshy columns, called _co-lum'nae
car'ne-ae_. The walls of the left ventricle are thicker and stronger
than those of the right.

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335. Of what is the heart composed? Give its divisions. 336. Describe
the auricles. 337. Describe the ventricles.

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338. The cavities in the right side of the heart are triangular in
shape; those of the left, oval. Each cavity will contain about two
ounces of blood. Between the auricle and ventricle in the right side
of the heart, there are three folds, or doublings, of thin, triangular
membrane, called the _tri-cus'pid_ valves. Between the auricle and
ventricle in the left side, there are two valves, called the
_mi'tral_. There are seen passing from the floating edge of these
valves to the columnae carneae, small white cords, called _chor'dae
ten'di-nae_, which prevent the floating edge of the valve from being
carried into the auricle.

339. The right ventricle of the heart gives rise to the _Pul'mo-na-ry_
artery; the left ventricle, to a large artery called the _A-ort'a_. At
the commencement of each of these arteries there are three folds of
membrane, and from their shape, they are called _sem-i-lu'nar_
valves.

340. The heart is supplied with arteries and veins, which ramify
between its muscular fibres, through which its _nutrient_ blood
passes. It has, likewise, a few lymphatics, and many small nervous
filaments from the sympathetic system of nerves. This organ, in its
natural state, exhibits but slight indications of sensibility, and
although nearly destitute of the sensation of touch, it is yet,
however, instantly affected by every painful bodily excitement, or
strong mental emotions.

_Observation._ To obtain a clear idea of the heart and its valves, it
is recommended to examine this part of an ox or calf. In order that
each ventricle be opened without mutilating the fleshy columns,
tendinous cords, and valves, cut on each side of the septum parallel
to it. This may be easily found between the ventricles, as they differ
in thickness.

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338. How do the cavities in the heart differ? What is found between
the auricle and ventricle in the right side of the heart? How many
valves in the left side, and their names? Where are the tendinous
cords, and what is their use? 339. What vessels proceed from the
ventricles? What is said of their valves? 340. With what is the heart
supplied? What is said of i