omposed of two layers, and may be said
to form the framework of the rectum. One layer is composed of circular
muscular fibres, and the other of longitudinal muscular fibres. In a
similar manner you could make a sleeve out of fine circular rubber
bands; then bind them together by rubber strings extending lengthwise
of the sleeve. With the circular bands the bore of the sleeve may be
contracted or widened; and with the longitudinal bands the length may
be shortened or extended. Just so with the corresponding muscular
membranes of the rectum, in their normal and abnormal conditions.
Outside of the longitudinal muscular bands are the serous and areolar
layers, the latter covering the lower half of the rectum.

As you look inside the incomplete model of the rectum, or rather
sleeve, you observe circular muscular bands or fibres which it is
necessary to cover with soft spongy or fatty substance in whose meshes
are nerves, blood-vessels, etc. This is called the areolar layer or
coat. One more layer or coat upon this--the mucous coat--completes the
structure. This latter possesses the power of accommodating itself to
the distention and contraction of the muscular tube. The mucous
membrane is thrown into folds and columns which serve as valves to
inhibit the undue descent of the feces, thus assisting the mucous
membrane in performing its office.

The length of the rectum varies in different persons, six inches is the
average length. It is divided into two parts. The upper part is a
little more than three inches long; beginning in front of the third
sacral vertebra and extending down to the end or tip of the coccyx. In
shape this part conforms to the curve of the sacrum and the coccyx, to
which it is attached behind. The lower part of the rectum is a little
shorter than the upper part, and begins at the tip of the coccyx and
extends down with the same curve as the upper part, terminating at the
upper portion of the anal canal.

Returning to the sleeve again; the portion of it from the shoulder to
the elbow illustrates the upper part of the rectum when partially
covered with a serous coat on the side opposite the bore (the outside).
From the elbow to the wrist-band illustrates the lower part of the
rectum, when covered on the outside with an areolar coat.

The wrist-band of the sleeve will represent the anal tube if drawn into
a pucker and turned slightly backward from the direction of the sleeve
of which it is a continuation.