them. But on the whole, we usually find, that
in addition to much gaseous fluid, the cascum
of the healthy subject is partially distended
by pultaceous or semi-fluid contents. While
the colon is occupied at various points of its
length by matter, the faecal character of which
is still more distinct, and the consistence of
which gradually increases as it approaches the
rectum.

W here these rudimentary faeces are very im-
perfect, scanty, and interrupted, they only oc-
cupy some of the sacculi or cells of the bowel,
leaving its central or general calibre in an empty
state. But when better developed, they form
what is termed a " figured " mass. This con-
sists of a kind of central rod, that corresponds
to the general axis of the tube; and of processes
that come off from the sides of this axial por-
tion, and are contained in the rows of pouches
formed by the wall of the bowel. In short,
the solid and continuous faecal substance forms
a tolerably perfect cast of the bowel ; a cast
in which the sacculi of the colon are "figured "
as projections, themselves isolated by depres-
sions corresponding to the intersections of
its longitudinal and transverse bands.

The characteristic shape thus possessed by
the solid contents of the colon, is often retained
by the faeces which have been forced through
the rectum in the natural process of defaeca-
tion. And although it is often absent, the con-



STOMACH AND INTESTINE.



367



sistence of the faeces being such* as to mould
them to the cylindrical form of the last-named
portion of tube through which they have to
pass still it occurs so frequently in Man, and
so universally in many of those Herbivora in
whom we can best study the phenomena of a
highly developed large intestine, as to afford
a valuable testimony to the natural action
of this part. It is therefore difficult to avoid
believing, that the individual sacculi of the
colon, or at least of its later segments, retain
the faeces for a considerable period of time ;
during which they so far complete the action
of the large intestine upon these its contents,
as to leave nothing for its remaining segments
to effect, save their mechanical propulsion to-
wards the outlet of the canal. To this inter-
mittent action of the muscular coat in respect
of time, we may probably add a similar inter-
ruption as regards space. In other words,
the interrupted and irregular manner in which
the sacculi are often occupied by solid faeces,
entitles us to suspect, that different lengths of
the intestine can act independently of each
other. But it is difficult to hazard a con-
jecture as to whether the contraction of the
falciform transverse folds ever really shuts off
portions of the tube into distinct cavities.
The central axis of the figured evacuation is,
however, often so slender, or even interrupted,
as remarkably to corroborate such a view.
And some authors have assumed that the
caecum, during its digestive act, is isolated
from the ascending colon by a vigorous con-
traction of that large fold which is prolonged
from the frrena (or anterior and posterior
extremities) of the ilio-caecal valve.f

The little information afforded us by direct
observation on the movements of the intestine,
confirms what is thus vaguely suggested by
the appearances of its expelled contents. The
highly developed large intestine of the living
or newly-killed rabbit, rarely exhibits any
noticeable movement whatever, when first ex-
posed to the air. By and bye, however, a kind
of irregular peristalsis comes on. But this is
nowhere quite so energetic as that seen under
similar circumstances in the small intestine ;

* The consistence of even a figured evacuation is
sometimes so slight, as to render it highly probable,
that a general relaxation of that segment of in-
testine which originally contained the faecal mass
has accompanied the propulsive contraction of the
part immediately behind it. Such an apparently
co-ordinate relaxation of the muscular coat may be
frequently noticed in that vermicular movement
of the small intestine which is seen shortly after
death. An occurrence of this kind seems almost the
only way in which one can account for the fact,
that soft and semifluid faeces frequently retain the
form of the colon, after passing 'through its
falciform folds. Whether sucli an action is ever
effected by a contraction of the longitudinal bands
simultaneously with a relaxation of the circular or
falciform folds, it is impossible to determine. But
from their mechanism, and from the above appear-
ances of the faeces, it would seem more probable
that both these classes of fibres relax simultaneously.

f Energetic contraction of the transverse fibres
of this valve would obviously aid in its occlusion ;
though we have already shown it to be probably
independent of all active muscular force.



and is generally very feeble in the caecum.*
And in this movement, as in that produced
by mere local irritation, we may notice the
peculiar character before attributed to the
contraction of unstriped muscle generally ;
viz., that of diffusing itself over a time and
space greater than those occupied by the
irritation which has excited it. As regards
the details of this vermicular action, certain
sacculi contract and dilate alternately ; the
transverse constrictions between them shar-
ing in the same movement. This alternate
movement is often accompanied by an irregular
contraction of the longitudinal bands; which is
sometimes carried to such an extent, as to
shorten the tube, by approximating and di-
lating certain of its cells. And even where the
effect of the local irritation survives its cause,
so as to excite a continuous movement which
proceeds along a considerable length of intes-
tine, still it rarely affects all the cells of the
bowel exactly alike; but often passes lightly
over one or two, to bear with increased inten-
sity on those which immediately succeed them.
Very similar movements are produced by
galvanizing the solar plexus which gives off
the nerves to the large intestine.

On the whole, therefore, the greater solidity
of the contents of the large intestine implies
a greater resistance to the contraction of its
muscular coat. And the structure of this
coat shows no proportionate increase, but
rather a decrease of strength. Hence we
might almost conjecture, that the general
movement of the small intestine is here ex-
changed for one which is slower, feebler, and
hence less effective : and which, besides being
much weaker, is possibly interrupted by
longer periods of rest.y

But it is probable that this comparatively
feeble character of the general movement of
the large intestine is capable of being more
than compensated by that heightened efficacy
which the peculiar arrangement of its mus-
cular coat can concede. The thin muscular
stratum that forms the wall of its numerous
pouches, is evidently capable of assuming a
much smaller surface, in obedience to the
thick and powerful bands of its transverse
and longitudinal coats. Indeed, the simul-
taneous contraction of these two sets of
fibres would convert them into what would
form, for the time, a very thick and powerful
expanse of unstriped muscle, capable of ob-
literdting the entire calibre of the intestine.

In this way the same muscular apparatus

* The contractions by which this part responds
to a local stimulus are far more feeble, slow, and
uncertain, than those obtained in any other part of
the canal, the stomach not excepted. This character
seems to be a direct result of the tenuitv of the
muscular coat, which also attains its maximum here.
An incident which I have remarked in one or two
cases of intestinal obstruction appears to be partly
explained by the same structural peculiaritv. In
these instances, though the stricture was seated in
the descending colon, the dilatation and rupture
that formed the immediate cause of death occupied
the caecum.

t Compare pp. 343, 344,



368



STOMACH AND INTESTINE.



which generally concedes to the contents of
the large intestine a long delay, and a slight
movement over a large absorptive surface,
would still be quite capable of effecting their
rapid and vigorous expulsion, when required
to do so. Nay, more, since much of this ex-
pulsive act seems, as it were, removed from
the sacculi themselves, and concentrated in
the bands around them, we may conjecture
that the mechanism of these latter contrac-
tile masses is also specially concerned in the
nervous part of the process. At least, it is
not impossible, that the irritation or stretching
of these two sets of muscles (which can be
effected only by the general distention of the
calibre of the tube, and not by the local dis-
tention of its cells) may constitute the im-
mediate stimulus of the evacuation of the
whole large intestine, or of any particular
segment.

The mucous membrane of the colon may be
described as only differing from that of the
small intestine in the fact that it is somewhat
thicker, and quite devoid of villi. Its more
numerous tubes are about one-third longer
than those of the small intestine ; and their
diameter seems to be, in genera!, still more
increased. Its solitary follicles are also more
numerous, and of larger size. And the
depressions which mark the site of each on
the internal surface of the bowel are here
represented by a distinct pit ; which leads by
vertical, or even somewhat divergent sides,
to the follicle that occupies its base. But the
secretions of these structures, and the cell-
growth which lines them, do not present any
noticeable difference from their analogues in
the small intestine.

The rectum (/-, fg. 274. ; r 1, r 2, r 3, Jig.
276.) (formerly straight gut, Eng. ; Mastdarm,
Germ.), which intervenes between the sig-
moid flexure of the colon (s) and the anus
(w), forms the terminal segment of the large
intestine. It has received the above name
from the comparatively direct course which
it takes. Its length is about seven to eight
inches. Its width is at first only equal to
that of the small extremity of the colon,
with which it is continuous : but gradually
increases, so as to form a kind of dilatation or
pouch in the immediate neighbourhood of its
lower aperture. Here it suddenly contracts
to the narrow orifice of the anus ; which is
situated in the perineal space, that closes the
pelvis, and forms the lower extremity of the
trunk.

Strictly speaking, however, the rectum is
by no means straight. Beginning at the left sa-
cro-iliac symphysis (e,fig. 276.), it first passes
obliquely downwards and to the right side,
towards the median line of the trunk; which
it reaches at a point that nearly corresponds
to the body of the third sacral vertebra (at
r 1, fig. 276.). And though, from hence to
its termination, it continues to occupy the
middle line, still as it rests upon the concave
anterior surface of the remainder of the spinal
column, it assumes a curve similar to that of
the sacrum. It thus acquires a second and



more remarkable bend (at r 2, Jig. 276.), which
is convex backwards. Finally, at the tip of the
coccyx, it quits the antero-posterior direction
given it by this bone ; and, bending suddenly

Fig. 276.




The viscera of the adult male pelvis, as seen after
the removal of the right innominate bone : show-
ing the situation and relations of the rectum.

a, fourth lumbar vertebra; b, bladder; c, sym-
physis of the pubis ; d, inner surface of the left
osilii; e, sacro-iliac articulation;/, vasdeferens;
g, ureter ; h, spine of the ischium sawn through,
and left attached by the coccygeus muscle ; i, left
vesicula seminalis; " k, prostate gland; /, bulb of
the urethra ; m, left corpus .caveruesum divided at
its root ; n, anus ; o, levator ani cut across near its
attachment to the coccyx ; p. sciatic nerves and
vessels ; 9, fibres of levator ani passing round the
lower end of the rectum ; r, rectum, 1, 2, 3, its first,
second, and third portions ; s, sigmoid flexure of
the colon ; r v, peritoneum forming the left side
of the recto-vesical pouch.

downwards at a right angle, becomes vertical
for a very short distance (at r 3, Jig. 276.) prior
to ending in the anus.

The above successive changes in its di-
rection are associated with others, which af-
fect its relations to the peritoneum and to the
surrounding structures. In accordance with
these, it is usual to describe the rectum as
subdivided into three portions.

The first or oblique segment (between s
and r 1, fig. 276.) is about 3 inches long.
It is covered on every side by peritoneum ;
which, at its commencement, attaches it to
the pelvis by a short meso-rectum, very simi-
lar to the meso-colon of the sigmoid flexure.*
It lies on the sacrum, the upper border of
the pyriformis muscle, and the sacral plexus.
In front of it is the bladder, from which it
is generally separated by some convolu-
tions of the small intestine. On either side

* This meso-rectum is sometimes so long, as to
give this segment of the bowel a mobility (and often
a shape) very similar to that of the neighbouring
sigmoid flexure itself.



STOMACH AND INTESTINE.



369



it is related to the ureter, and to the branches
of the internal iliac vessels.

The middle or arcuate segment (r 2, Jig.
276.) scarcely exceeds 2f inches in length.
It lies on the sacrum and coccyx ; to which
it is attached by a loose areolar tissue, that
usually encloses much fat. The peritoneum,
which invests a small part of its lateral sur-
faces above, soon becomes limited to its
anterior surface as it descends; and ceases
altogether at a distance of about an inch
from the termination of this part of the
bowel. This incomplete serous covering
is, in fact, the lower extremity of a pro-
cess of peritoneum, which is called the recto-
vesicul pouch (r v, Jig. 276.). The apex of
this, below, corresponds to the point where the
membrane is reflected from the anterior sur-
face of the rectum, to the neighbouring pos-
terior surface of the bladder. Hence the front
of the bowel, which, above, comes into contact
with the distended bladder, or with any con-
volution of small intestine that may chance to
occupy the recto-vesical pouch, touches, be-
low, the anterior part of the base of the blad-
der. This it does in a triangular space, that
is bounded on each side by the vesicula semi-
nalis (i, fig. 276.), and behind by the pouch
aforesaid : a space, which therefore corre-
sponds to the "trigone vesicate" on the inner
surface of the bladder ; and marks a region,
where this viscus may be punctured through
the rectum, without any injury to the serous
membrane. On each side of this part of
the rectum, is a lamina of pelvic fascia which
supports it; and externally to this is the
coccygeus muscle, which descends from the
spine of the ischium (h,fig. 276.) to the bor-
der of the coccyx.

The third or terminal portion of the bowel
0' 3 '/g- 276.) is about 1| inches long. It is
surrounded, above, by areolar tissue loaded
with fat: below, by the sphincter ani externus
(at n}- and by the levator ani (o and q} which
descends from the pelvis to mingle its fibres
of insertion with those of the former muscle.
In front of it are the prostate (k,fg. 276.)
and the membranous portion of the urethra in
the male, the vagina in the female: behind it,
the tip of the coccyx in both sexes. The
degree in which the prostate projects into the
rectum will of course vary, both with the size
of this gland, and with the amount of dis-
tention to which the tube itself is habitually
subjected. Where its distention is very great,
the flaccid intestine sometimes appears almost
folded around the prostate gland, so as to
offer a kind of pouch on either side of it.

As regards the structure of the rectum, its
peritoneal coat has already received a sufficient
description. Its muscular tunic differs remark-
ably from that of the colon. In place of being
divided into three bands, the fibres of the longi-
tudinal coat are again collected into a single
uniform expanse, that surrounds the wholeof
the tube. And both it and the transverse layer
are very much increased in thickness. Thus
even in the upper part of the rectum, the
muscular coat offers a total thickness which at
Supp.



least doubles that of the colon; while near its
termination, it is scarcely less than four times
as thick. The fibres themselves are of a red-
der colour, especially the transverse; and near
the anus, they are mingled with the striated
elements of the adjoining voluntary muscles.
And that distant analogy which the rectum
seems to offer the oesophagus in all these
respects, is rendered somewhat closer by
the presence of numerous folds of mucous
membrane, which the mere passive contrac-
tion of its muscular tunic appears generally
to produce. In short, it would hardly be an
exaggeration to say that this, the last segment
of the digestive canal, resumes not only the
median position, but even the structure and
action, of the first.

Muscles of the anus. The muscular appa-
ratus that guards the lower outlet of the rec-
tum, consists chiefly of two sphincter muscles,
which close the orifice of the anus by their
contraction. Of these, one, the sphincter
ani internu-Sy which is situated within the
bowel, is little more than a thickening of
the proper transverse or circular layer of its
muscular coat. It lies immediately beneath
the mucous membrane, and consists of the
ordinary unstriped fibres, which retain their
usual pale colour. The other, the proper
sphincter, or the sphincter ani externus, is a
deep-red mass of striated muscular fibre,
which surrounds the lower extremity of the
rectum (at w, Jig. 276.), including the pre-
ceding structure. Its form is elliptical and con-
cave; so that its outer border occupies a higher
level than its inner one. Hence it receives the
end of the bowel as it were into a shallow
funnel; and, on contracting, occludes its
cavity by the pressure of what is a surface,
and not merely an edge, of its plane of fibres.
Its outermost bundles arise from a tendinous
structure which is prolonged from the tip of
the coccyx; and they pass forwards, on both
sides of the bowel, to reunite in the central
tendinous point of the perinaeum. Its inner-
most or lowest fibres are attached to a dense
subcutaneous areolar tissue that lies before
and behind the anus. In the female, they
interlace anteriorly with those of the con-
strictor vaginae, by what is often a distinct
decussation.

It is chiefly through the intervention of this
sphincter that the levator ani muscle is con-
nected with the lower extremity of the rec-
tum. The fibres of this large expanse of
striped muscular substance descend from their
pelvic origin*, with an inclination backwards,
to reach the lower orifice of the cavity of the
pelvis, which they assist to close. In front
of the rectum, a certain number of them are
inserted into the tendinous and areolar tissues
which here occupy the middle line of the peri-
neum ; and these join more or less directly
with the attachment of the external sphincter
in the same situation. Behind the rectum, a
considerable plane of the more posterior fibres

* For a fuller description of the origin and rela-
tions of the above muscle, the reader is referred to
the Article PELVIS.

B B



370



STOMACH AND INTESTINE.



of the levator passes around the tube, return-
ing upon itself in the similar portion from the
opposite side, so as to sling and sustain the
canal. Between these anterior and posterior
slips, is a median portion ; which descends to
be inseparably united with the upper and outer
rings of the external sphincter itself. And
besides interlacing with the striped fibres of
this muscle, it mav generally be traced sending
off a certain number of its scattered bundles,
to decussate and disappear amongst the un-
striped fibres of the longitudinal and transverse
layers of the rectum just at their termination.

Movements of the rectum. The contraction
of the muscular coat of the rectum, like that
of the other segments of the digestive tube,
has for its object the onward propulsion of its
contents. But since the rectum ends the intes-
tinal canal, it forms the portal by which these
contents are altogether dismissed from the
body. Health and comfort alike require that
this act of dismissal should be both inter-
mittent and infrequent. While the mere con-
sistence of the faeces is generally such as to
demand the application of a comparatively
powerful force in order to effect their rapid
removal. Hence the entire mechanical action
of the rectum is naturally divisible into two
stages : one which propels, and one which
expels, the various substances occupying its
interior. The latter of these two processes
is called defecation ; and, as we shall see, in-
volves the aid of various agents which are
strictly extraneous to the bowel itself.

Those movements of the rectum which are
seen in living or newly-killed animals, can only
be regarded as confirming the conclusions that
might fairly be inferred from the much greater
thickness of the muscular coat in this particu-
lar segment of the large intestine.

When empty, the bowel remains in a state
of rest, from which it can scarcely be aroused
to peristalsis by the application of any local irri-
tation. But when occupied by a moderate quan-
tity of faces, it will often respond to a direct
mechanical stimulus ; and still more energetic-
ally to the electrical irritation of its nerves.
On applying the rapid and powerful shocks of
the electro-magnetic machine to those large
branches of the sympathetic which are distri-
buted in the muscular coat of the rectum, a
violent contraction of this tube frequently
occurs. In this intense but irregular move-
ment, we may generally observe a shortening
and a constriction : acts which no doubt re-
present the specific contractions that form the
functions of the longitudinal and transverse
fibres respectively. Thus the bowel suddenly
becomes straighter and shorter; and hence
appears as though it were jerked downwards
towards its most fixed point at the lower open-
ing of the pelvis. This shortening is generally
accompanied by a less violent and more uniform
movement: in short, by a peristalsis; which
offers the ordinary progressive cons'riction,
and is evidently the principal agent in the pro-
pulsion of the fecal pellets. But both of these
movements are very irregular. The former
commonly alternates with a relaxation, which



appears to pull the rectum upwards, and exag-
gerate its curves. While the latter occupies
various parts of the bowel with very unequal
intensity and duration; and, occasionally, even
seems to take a retrograde course. In most of
these details, we may observe the same close
analogy between the rectum and the oesopha-
gus, which has already been remarked in their
median and terminal situation, and (to a
lesser degree) in the nature and thickness of
their muscular coat.

The normal movement of the bowel differs
from the above in the fact of its being a more
exact and co-ordinate action ; and, therefore,
a much more effective one. But while obser-
vation and experiment both agree in repre-
senting it as a peristalsis, which is quite capable
of slowly expelling faeces of moderate consist-
ence, no'thing is more certain than that it is
rarely called upon to exert such an inde-
pendent and unaided force.

Under all ordinary circumstances, its influ-
ence is assisted by the action of various vo-
luntary muscles. These ma} be divided into two
classes, which differ in their situation and action.

The first are those large planes of muscle
which form the anterior, lateral, and superior,
walls of the belly; and thus, by their contrac-
tion, exert a forcible pressure on the intestines
contained in this cavity.

The second are the similar structures that
close the outlet of the pelvis. These have for
their office to support the end of the canal.
And their muscular nature enables them to
effect this support by a texture, the passive or
active contraction of which can always increase
the reaction or resistance to the abdominal
pressure in exact correspondence with the
varying demands made upon it. They thus fix
the end of the intestinal canal, while it is
being emptied of its contents by the pressure
of the muscles of the belly.

The mechanism of the abdominal pressure
having already been described in treating of
the act of vomiting*, but little need here be
added with reference to the special conditions
under which it is called upon to aid that of