clusively for the growth and renovation of
the system, are found only in the alimentary canal. They are called
lacteals. The vessels whose sole function is to remove particles of
matter already deposited, are called _Lym-phat'ics_. The radicles, or
commencement of the veins, in many, and it may be in all parts of the
body, perform the office of absorption.

_Observation._ This fact accounts for the capacity of the venous
system exceeding the arterial. Had the veins no other function to
perform, beside returning the blood that had been distributed by the
arteries, it would be reasonable to suppose that this system would be
less than the arterial, but the reverse is known to be true.

389. The LYMPHATIC VESSELS, in structure, resemble the lacteals. They
exist in great numbers in the skin and mucous membranes, particularly
those of the lungs. Though no lymphatics have been traced to the
brain, it is presumed that they exist there, as this part of the body
is not exempt from the composition and decomposition, which are
perpetual in the body. These vessels are extremely minute at their
origin, so that in many parts of the system they cannot be detected
without the aid of a microscope.

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387. Define absorption. 388-391. _Give the anatomy of the lymphatic
vessels._ 388. What are those vessels called that act exclusively for
the growth and renovation of the body? Those whose office is to remove
the atoms already deposited? What other vessels perform the office of
absorption? Give observation. 389. Describe the lymphatics.

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[Illustration: Fig. 82. A single lymphatic vessel, much magnified.]

[Illustration: Fig. 83. The valves of a lymphatic trunk.]

[Illustration: Fig. 84. 1, A lymphatic gland with several vessels passing
through it.]

390. The lymphatic vessels, like the veins, diminish in number as they
increase in size, while pursuing their course toward the large veins
near the heart, into which they pour their contents. The walls of
these vessels have two coats of which the external one is cellular,
and is capable of considerable distention. The internal coat is folded
so as to form valves, like those in the veins. Their walls are so
thin, that these folds give them the appearance of being knotted.

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What is represented by fig. 82? By fig. 83? By fig. 84? 390. In what
respect do these vessels resemble the veins of the system? Give