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202 ANATOMY.

rod-like, or irregular, and in whose interior Ave can make out, by proper
handling, (1) small definite bodies, the nucleus corpuscles; (2) a net-like
framework of nucleus substances ; and (3) a clear fluid, the nucleus
juice. The young cell is at first naked ; only in its matured stages does
it develop on its surface an optically distinct membrane or other struc-
ture according to the .special tissue of which it forms a part."
The cells of the embryonal jNIalpighian layer dip down into the
subepithelial connective ti.ssue (the coriura) and form epithelial biids,
which are the commencement of the mucous glands, although varying
in shape according to their locality and function. The glands, judging
from the nature of their epithelial lining, can be described under
three general modifications : I. Simple tubular mucous glands ; II.
Compound tubular mucous glands; III. Compound tubular salivary
glands.
I. Simple Tubular Mucous Glands (Fig. 98).—The crypts or
follicles of Lieberkiihn that are found in the intestinal canal may be
taken as typical glands of this class. They
usually present the shape of a te.st-tube, form-
Fig. 98.
ed of the epithelium, the csecal end pushing
the basement-membrane into the corium or
substance of the mucous membrane, the tube
opening on the surface. The cells lining the
tubes are of a single layer, and apparently of
the same character and continuous with the
columnar epithelial cells of the surface. They
are well distributed within the mucous mem-
brane, varying in number and kind accord-
ing to locality. They are generally placed
perpendicularly to the surface, and often close
together, in which position they constitute the
bulk of the mucous membrane, the thickness
r
of the membrane often depending ujion the
length of the tubes, which differs in different
IJn^ localities. The cells are short, cubical, or
columnar, pos.sessing a spherical or oval nu-
---^ -- - - - '' cleus. Although the gland-tubes are usually
single, somc the deep ex-
From a vertical section throuKh are bifurcatcd at
trcmity, aud thcjowcr end may be somewhat
jIlVe^'Mt"esti,'esT.V'aD^^^
iiig, (», the crypts i)f Lielierkiihn enlarged in its diameter.
closely placed side by side, each
crypt lined with a layer of The.se glands are found in large numbers in
coluninar epithelium;' jnm,
muscularis inticosse .v, sub- the stomach, large and small intestines, and
;
miicosK.
the uterus.
Simple tubular glands occasionally have their secreting surfaces
increased by becoming pouched or loculated.
II. Co:^rpoT^ND Tubular Mucous Glands.—The mucous glands
found in the mouth and the glands of Brunner in the intestines are
typical of this class, being small racemo.se glands. Tlie.se glands open
upon the surface of the mucous membrane with a funnel-shaped mouth,
from which a duct passes in an oblique direction (the angle of obliquity
not always being the same) through the corium into the submucous