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200 ANATOMY.

oral cavity, or be continuously subjected to the action of the fluids of the
mouth, it will take upon itself the functions and cliaracteristies of mucous
membrane, assuming- greater translucency, its cells becoming compara-
tively thin, some of them having small nuclei.
In the olfactory portion of the nasal chamber, the upper part of the
pharynx, also in the larynx, trachea, and bronchi, the cellular invest-
ment is made up of stratified cylindrical ciliated epithelium.
The epithelial cells of the nuicous membrane are slightly separated,
but, like those of the skin, are held together by an intercellular cement
substance, and it is through this cement substance that absorption
(very slight) takes place when medicaments are placed either on the
skin or nuicous membrane ; as they pass through they enter the lymph-
spaces in the areolar connective tissue, and in this way get into the cir-
culation through the larger lymphatics.
The Cor'nim of the mucous membrane lies immediately beneath the
basement-membrane, but is not always demonstrable. It is made up
very similarly to the corresponding layer of the skin— /. e. of areolar
connective tissue, sometimes containing a large intermixture of lymphoid
tissue. It also contains white and yellow fibrous connective tissue,
muscular tissue, vessels, lymphatics, and nerves. The corium varies in
thickness according to its locality. In the oesophagus, bladder, and
vagina the fibrous tissue is abundant, forming almost a compact web
and making the mucous membrane of these parts somewhat stout and
tough. In other parts, as in the stomach and intestines, the tissue is
retiform or lymplioid, lacking the white elastic tissue. Along the side
and beneath the tongue in the alveolo-lingual groove, also at the base
of the tongue and the epiglottis, and from that to the side of the pharynx,
the corium is exceedingly loose and pliable.
On the alveolar processes of the inferior and superior maxillary bones
this layer is made up of dense connective tissue, and is firmly attached
to the membrane immediately upon the bone which forms the gum tis-
sue or mueo-})eriosteum (Allen). This muco-periosteum has both the
function of nuicous membrane and periosteum, and it is througli it
tliat the bone receives nourishment. AVhen the membrane is lost or
destroyed, necrosis takes place the same as in bones which are supplied
with a true periosteum. Where cartilage is covered by mucous mem-
brane, as in the septum of the nose. Eustachian tubes, the larynx, etc.,
it is called nuico-perichondrium (Allen), and acts as a nourisher and pro-
tector to the cartilage similarly to the ])erich()ndrium of cartilage.
Upon the hard palate the muco-periosteum is united by a fine
trabecula to the ridges of the bony surface. In the interspaces and
within the muco-periosteum there are small racemose glands. Upon
the soft palate it is more firmly adherent at the anterit)r surface than
tiie posterior, where it comes in contact with the gland tissue. It is
found on the roof of the pharynx attached to the aponeurotic membrane
of the base of the skull, and upon the tongue it is firndy attached and
forms the cortex.
Blood-vessels of the mucous membrane are generallv very abundant.
The brandies of the arteries and veins divide and subdivide in the sub-
mucous tissue as in the skin, and pass into the corium, where they again