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328 ANA TOMY.

rise to a beaded appearance. They are not farther apart than -^ to
\ inch. The superficial vessels are most abundantly supplied with
valves, those of the arm containing from sixty to eighty between the
fingers and axillary glands, while the corresponding vessels of the
lower limbs contain from eighty to one hundred. The valves are
generally arranged in pairs, and consist of two semilunar folds, with
their concavities directed toward the larger vessels. They are formed
by a reduplication of the lining membrane, the two folds being strength-
ened by fibrous tissue from the middle coat.
Lipaphatic (rlaiuh.—The lymphatic glands are small lenticular bodies
placed along the course of the lymphatic vessels as they pass from their
points of origin toward the thoracic duct., They are exceedingly numer-
ous, the total number being estimated at from five to seven hundred.
They vary considerably in size, some not being larger than a pin's
head, while (jthers attain a size equal to that of a kidney bean. As the
lymphatic glands are in connection ^vitll the vessels, they may, like them,
be divided into a superficial and a deep set ; the former are most
abundant around the head and neck and at the lines of union of the
limbs with the body; the latter are found most abundantly in the
thorax and abdomen along the course of the deep-seated vessels. The
glands situated between the folds of the mesentery are kno\\'n as the
mesenteric glands. The lymphatic vessels as they approach a gland
break up, before entering it, into a number of small branches—the
vasa afferentia, which penetrate its investing membrane. From the
opposite side of the gland the lymphatics again emerge, as the vasa
efferentki, and a short distance beyond it unite to form trunks larger,
but fewer in number.
The lym])hatic glands present at one point a depression which is
termed the hilum, through which the blood-vessels pass into and out
of the gland, and through which
Pjj^, J--
also emerge the efferent vessels.
Except at the hilum the gland
is entirely covered externally by
a membrane composed of dense
connective tissue. The interior
of the gland is soft and pulpy,
of a dark color, and mottled in
a])])earance. The superficial })art
of the gland is termed the corii-
cdJ, the dee])er \yay\ the medullary
])()rtion (Fig. loo).
From the inner surface of the
Section of Small Lyiiipliutic (ilaiid, half cliaRrain-
niatically ^'nan, with the course of tin- lyinjih : investing membrane there pass
a. the envelope; h, septa between the follioh's or inward partitions or septa of
alveoli of the cortical part; r-, system of scjita of
the nieduilary portion (h)wn to "the hilum; follicles; />, lymph-cords of thi' mcilullary mass; f.
atl'erent lymph-vessels, the diliiMent lymphatic which divide the outer zone of
streams from which surround the follicles and
the gland into small comj)art-
flow throuf;h the interstices of the medullary jior-
tion ; (/.continence of these to pass throuf,'ii tlie ments, which are conical in
etferent vessel (h) at the hilum.
shape in consequence of the
convergence of the partitions toward the centre of the gland. These