r P- * P- 8 - tained in the cavity of the uterus.
STOMACH AND INTESTINE.
to allow of the much quicker destruction of
their poisonous properties by a more or less
perfect oxidation.
Arteries of the intestines. We have seen
that the stomach and duodenum are supplied
with arterial blood by means of various twigs
derived from the three branches of the coeliac
axis, which springs from the upper part of
the abdominal aorta. The remainder of the
intestinal canal is furnished with arteries which
are given off by two large branches of the
abdominal aorta. These branches are named,
from their position and distribution, the
superior and the inferior mesenteric.
The superior mesenteric artery (a, fig. 277.),
the longer of these two branches, is distributed
over that large segment of the intestine which
is formed by the lower part of the duodenum,
the whole of the jejunum, ileum, and ccecum,
and the first two-thirds of the colon. The
Fig. 217.
Distribution of the superior mesenteric artery to the
small and large intestine.
a, trunk of the superior mesenteric artery ; b, ileo-
colic artery ; c, its iliac branch ; d, its colic branch ;
e, right colic artery; /, middle colic artery; g,
arches formed by the anastomosis of the branches
to the small intestine ; p, pancreas ; du, duodenum ;
j, jejunum; i, ileum ; c ee, caecum; ac, ascending
colon ; t c, transverse colon ; d c, descending colon.
trunk of the vessel comes off from the aorta,
at a point which about corresponds to the
upper border of the second lumbar vertebra.
It is separated from the coeliac axis by the
pancreas ; and hence is distant about a third
of an inch from the origin of the latter vessel.
From this commencement, it passes down-
wards and forwards, crossing over the termi-
nation of the duodenum, so as to reach the
upper part of the mesentery. It now con-
tinues downwards between the two layers of
this fold of peritoneum, which it occupies near
379
its attachment to the posterior wall of the
abdomen. Hence its length and direction
correspond to those of the attached border of
the mesentery itself ; and are such, as to
conduct it downwards and obliquely towards
the left side, to a termination that corresponds
to the end of the ileum, or the commencement
of the coecum. But the branches given off to
these latter segments of the intestine by the
trunk of the vessel are so large, and so directly
continuous with its previous course, that it is
only in a very arbitrary and limited sense that
we can speak of it as ending in this situation.
The arrangement of the larger or primary
branches of the superior mesenteric artery
is liable to great variation, but is generally as
follows.
The trunk of the superior mesenteric artery
is directly continuous with a large vessel (6,
Jig. 277.), which, when it has reached a dis-
tance of about two inches from the coecum,
divides into two others; of these the upper
(d,fig. 277.) passes towards the ccecum, and the
lower (c,fig. 277.) towards the ileum. Thei/eo-
colic artery (b,fig. 211. \ as the common trunk
is named prior to its bifurcation, usually gives
off from its right side one of rather smaller size,
about three inches from the border of the bowel.
The latter, which is called the arteria colica
dextra, or right colic artery (e,Jig. 277.), often
arises by a separate trunk from the superior
mesenteric. It takes a course almost horizon-
tally outwards, or towards the right side,
lying underneath the single layer of perito-
neum which covers in the ascending colon, so
as to reach this part of the large intestine at or
near the middle of its height. Finally, at a dis-
tance of little more than an inch from its
entering the mesentery, the trunk of the supe-
rior mesenteric artery gives off a large branch,
the arteria colica media (f,Jig. 277.), which
passes upwards and back wards, enters between
the two layers of the transverse meso- colon,
and is distributed to the transverse colon,
which it reaches at the middle of its posterior
border. Besides these named branches, the
superior mesenteric gives off numerous arte-
ries (at g, fig. 277.), of almost equal size,
which have not received any special designa-
tion. These twenty or thirty branches leave
the left side of the artery, at various points
between the lower border of the duodenum
and the origin of the ileo-colic artery ; and
pass outwards, or to the left side, towards
their distribution on the small intestine.
The further course of all these branches
towards the small and large intestine affords
a remarkable ; instance of an arterial ana-
stomosis ; such as is almost unparalleled in
the whole of the body for the freedom and
frequency of its communications, and the
size of the^vessels by which they are effected.
Each of the primary branches just alluded to
bifurcates: and its two resulting branches
unite with those above and below them, so
as to form a set (g,/g-277.) of arterial arches ;
from the convexity of which spring new
trunks, to divide and inosculate in a similar
manner. This arrangement, which prevails
380
throughout all the mesenteric branches that
supply the intestine, is carried to such an ex-
tent in the jejunum and ileum, as to offer, in
many parts, four or five successive sets of
arches ; which become smaller and more nu-
merous as they approach the bowel, and finally
give off the minute arterial ramifications that
enter and traverse the intestinal coats.
On reaching the intestine itself, the greatly
diminished arteries break up into still smaller
capillary branches. These inosculate freely
with each other, by comparatively large
branches of communication ; and thus unite
and anastomose to form a dense stratum or
flattened network of vessels, which occupies
the layer of loose areolar tissue that separates
the muscular from the mucous coat. This vas-
cular plexus gives off, on the one hand, the
vessels of the mucous membrane ; and on the
other, the not very numerous branches which
run between and amongst the unstriped bun-
dles of the muscular coat.
The inferior mesenteric artery (6, fig. 278.),
which supplies the descending and sigmoid
portions of the colon, and the whole of the
rectum, is also a branch from the aorta. It
arises from the front and left side of this
vessel (a, fig. 278.), about an inch below the
place where it gives off the left renal artery,
and nearly the same distance above its bi-
furcation into the two iliac vessels. From
this origin it is directed downwards and
slightly outwards, lying successively on the
aorta, the left psoas muscle, and the left
Fig. 278*
STOMACH AND INTESTINE.
Distribution of the inferior mesenteric artery to the
large intestine.
a, abdominal aorta ; b, inferior mesenteric artery ;
c, left colic artery ; d, artery to the sigmoid flexure ;
e, superior hsemorrhoidal artery; /, middle colic
artery; g, large communicating branch between the
left and middle colic artery, sf, sigmoid flexure
of the colon ; r, rectum, (t c, a c, p, du, as in
fig. 279.)
* In several of the preceding microscopic figures,
the artist has been indebted to Koelliker's beautiful
woodcuts for some details, which require this spe-
cific acknowledgment.
common iliac artery. During this part of its
course, it lies at some distance from the in-
testine. But below where it crosses the com-
mon iliac vessels, it occupies the double fold
of peritoneum (mesa-rectum) that attaches the
rectum to the pelvis. This terminal portion
of the vessel, which is called the superior hce-
morrhoidal artery (e,fig. 278.), is continued to
a point about opposite to the middle of the
sacrum ; where it ends by bifurcating into
two branches, which ramify on the opposite
sides of the bowel, and are distributed to
its various coats. These branches inosculate
freely with the ramifications of the middle
hcemorrhoidal artery, which is itself given off
to the rectum by the internal iliac artery, or
some of its branches.
The only named branches of the inferior
mesenteric are the left colic or arteria colica
sinistra (c, fig. 278.), and the artery to the
sigmoid flexure (d,fig. 278.). The former of
these two vessels passes upwards and out-
wards, across the psoas muscle and left kidney,
to reach the descending colon at about the
middle of its height. The latter, which is
sometimes double, also crosses the psoas, to
enter the short meso-colon which attaches
the sigmoid flexure of the bowel. The fur-
ther distribution of both these arteries pre-
cisely recalls that of the similar colic branches
from the superior mesenteric : each bifurcating
into two branches ; which, by uniting with the
similar trunks above and below, form the
origin of a set of arches that ramify in a second
and third series. And as the union of the
upper twig of the colica sinistra with the
lower or left branch of the colica media
unites the superior and inferior mesenteric arte-
ries by a large anastomosing vessel (g,fig. 278.),
all the arches of both these trunks have the
most complete anastomosis with each other.
So that it would be easy to trace out a con-
tinuous arterial channel of large size ; which
begins as the superior mesenteric, and passes
through the ileo-colic, left colic, median colic,
and sigmoid branches, to end in the superior
haemorrhoidal artery.
Veins of the intestines. The veins of the
intestinal canal are chiefly characterized by
the fact, that the trunks formed by their
convergence and union do not open into the
right auricle, like the veins of the body gene-
rally ; but undergo a second ramification and
distribution, in their course from the capil-
laries of the intestine to the right side of the
heart. This arrangement of course influences
their distribution at two successive stages of
their course. In the first place, their 'larger
trunks fail to exhibit that close correspond-
ence with the arterial channels which is seen
in the case of most other parts of the body.
And, secondly, instead of seeking the large
vessels on the spine, these trunks converge
into a single channel, the portal vein (, fig.
279.), which passes upwards to the liver at
some distance from the aorta and primary in-
testinal branches,*
* See Art. VENOUS SYSTEM.
which leave the intestine, and gradually unite
into the vessels that converge to form the
various trunks. These branches have a tole-
rable correspondence with the primary rami-
fications of the arteries from the coeliac axis
and the two mesenteric vessels. Many of
Fig. 279.
STOMACH AND INTESTINE. 381
The veins of the intestines commence by a third portion of the duodenum, it swerves
dense network, that receives the minute towards the right side, from what was hitherto
venous radicles into which the capillaries of an almost vertical course upwards ; and after
the mucous and muscular coats return their crossing in front of the duodenum at nearly
blood This plexus has the same submucous a right angle, ends by joining the splenic vein
situation, and flattened shape, as^ the cor- behind the pancreas. This junction glv es
responding arterial network already men- rise to the portal trunk (a, fig. 279.).
tioned; but, like the venous system in general, The inferior mesenteric vein (e, fig. 279.),
is composed of more numerous and larger -the origin of which also corresponds to the
branches. It gives off a number of veins ; region supplied by the artery of the same
name generally commences as a single trunk
at or near the border of the pelvis. From
hence it ascends almost vertically, but with a
slight inclination inwards, beneath the perito-
neum, and on the psoas muscle ; until, finally,
it crosses under the transverse meso-colon, to
end by a junction with the splenic vein (rf,
Jig. 279.). In the latter part of this ascent,
it is of course unaccompanied by the inferior
mesenteric artery : and even below where
this vessel is given off from the aorta, the
artery and vein diverge so as to be compara-
tively distant from each other. Its j'unction
with the splenic vein (d,Jig. 279.), is usually
about one or two inches from the point where
this meets with the superior mesenteric vein.
But it occasionally approaches much more
closely to the latter vessel, or even joins
with it prior to its union with the splenic to
form the portal vein.
The branches of both these mesenteric
veins resemble those of the corresponding
arteries in their number and size, and in the
remarkable freedom of their anastomosis. And
this copious and frequent inosculation, which
coincides with an absence of all valves,
not only holds good of the several primary
branches which converge into the portal vein,
but also applies in some degree to those
smaller ramifications, by which the portal sj^s-
tem inosculates with the general venous sys-
tem at the two extremities of the alimentary
tube. Thus many of the smaller veins at the
lower part of the oesophagus communicate with
both the azygos and portal veins. While the
Branches of the portal vein.
a, trunk of the portal vein ; 6, superior mesenteric
vein ; c, inferior mesenteric vein ; d, splenic vein,
joined by the, e, gastro-epiploic and pyloric veins ;/,
pancreatico-duodenal veins ; </, branch of the portal
trunk to the left lobe of the liver ; h, similar branch
to the right lobe.
(The remaining letters indicate as in the pre-
ceding figures.)
them unite to form two chief trunks, the
superior and the inferior mesenteric veins.
While others open directly into the splenic
vein ; or into the vena portce, which is formed
by the junction of it and these mesenteric
veins.
The superior mesenteric vein (b, jig. 279.),
which receives the venous blood from that
portion of intestine supplied by the artery of
the same name, travels for some distance in
company with the latter vessel ; lying on its
right side, and somewhat superficially to it,
and surrounded by very numerous lacteals and
nerves. But near the lower border of the
lowest branches of the inferior mesenteric vein
establish a similar and much more extensive
anastomosis of the two systems, by their junc-
tion with a dense venous network the hce-
morrhoidal plexus which encircles the lower
part of the rectum, and gives origin to the
middle and inferior hcemorrhoidal branches
of the internal and external iliac veins.
The foregoing peculiarities in the vascular
arrangements of the human alimentary canal
are at present only susceptible of a very im-
perfect explanation.
As regards the arteries, their great number
and size, and their large anastomosing chan-
nels, would probably be attended by several ad-
vantages. The variety of these channels would
concede to the circulation, not only a large
supply of blood, but one such as no ordinary
local accident could at all interfere with.* The
muscular fibre contained in their walls would
allow these numerous tubes to exercise an
unusual control over the amount of blood
* Compare the remarks on the vessels of the
stomach at p. 327.
382
STOMACH AND INTESTINE.
they from time to time convey. While on
very simple hydraulic principles, these re-
peated cross branches would so diminish the
various resistances (of impact and adhesion)
offered to the blood within the vessels, as to
permit, either a greater rapidity of the cur-
rent, and hence a more rapid renewal of the
mass of blood contained in the capillaries ; or
a more forcible pressure upon the latter fluid ;
or even both of these effects simultaneously.
It is perhaps a corroboration of the above
conjectures, to trace their close relation to
those which might be gathered from an inde-
pendent consideration of the circumstances of
the portal system. The trunk vein of this set
of vessels leads to a second set of capillaries
in the liver ; through which there is nothing
to propel the portal blood, save the force of
the heart, aided by a small amount of suc-
tion, which the thorax exerts as it ex-
pands during inspiration. And hence, how-
ever large a quantity of the original cardiac
pressure may be again amassed by the con-
vergence of the various intestinal veins, still
there can be no doubt that at least so
much of it will have been lost, as to require
all the aid which the above disposition of the
arteries can afford it. But in spite of all such
assistance, it seems probable, that the current
of the portal blood is both far slower, and
much more feeble, than that which occupies
any of the arteries. Still it is no doubt quite
sufficient for the exigencies of the circulation
in the liver; and especially for that secretion
of bile, to which the various details of the
organization of this gland chiefly refer.
THE FOOD. The function of digestion has
for its chief object the replacement of that
loss of substance which the body is con-
stantly undergoing.
Even the hardest materials of the globe we
inhabit experience a gradual disintegration ;
as the result of the various physical processes
to which they are exposed. Such processes
may be instanced in the attrition and solution
of solids, the evaporation of liquids, and the
diffusion of gases. And hence, when we turn
from these inorganic substances to the animal
fabric ; and consider its slight cohesion, the
friction which its locomotion implies, its
large watery constituent, and the feeble
chemical affinities which enchain its elemen-
tary atoms we shall scarcely be surprised
to find, that the rapidity of its waste far ex-
ceeds that of the inanimate solids around us.
But the rate of waste, and the consequent
need of replacement, both depend, far less on
simple physical causes of this kind, than on
certain actions which are specific to the or-
ganized body. These actions, which, in the
aggregate, make up what we term LIFE, do not
so much imply, as actually consist in, a per-
petual process of flux and metamorphosis.
This multiform change engages the whole of
the corporeal tissues; and conducts their
various ingredients, through a number of suc-
cessive phases of composition, to an effete and
useless state, in which they are finally ejected
from the organism.
And hence, whatever the share taken by the
physical actions of diffusion, solution, fric-
tion, and evaporation, in the removal of the
substance of the body, they are not in any
sense the true causes of its process of waste ;
or the real sources of its egcsta or losses.
They are but, as it were, the janitors of the
animal fortress ; the nature and amount of
the matters which pass out by them being
controlled and regulated by the higher life that
rules within.
The ingesta, which replace these egesta,
and thus form the opposite extreme of nu-
tritional life, are equally influenced by the
general requirements of the animal. Ex-
cluding, for the present, all consideration of
that preponderance of absorption which de-
termines the growth of a young animal, or
the converse excess of excretion which results
in the decrease and decay of an old one ; and
limiting our attention to the mere maintenance
of the adult body : we shall find that it is the
composition of its structures, and the rate of
their wear and tear, that chiefly determine the
kind of food it makes use of, and the quantity
it consumes within a given space of time.
While as regards the exact degree of this
dependence, we shall further find that, here
as elsewhere, the operations of organized
nature are only limited by wide general prin-
ciples ; within which are apparently conceded
great variety and fluctuation. The laws of nu-
trition are, so to speak, universal in their
range, but elastic in their application.
In respect to the nature of the food, we
may first notice, that by far the larger part of
it is always derived from the organic, and
never from the inorganic, world. In other
words, the chemistry of the organism has
little power of construction or synthesis.
So that, although a proximate analysis of the
tissues of the animal body presents us with
compounds, which may be shown to consist
chiefly of a few elementary substances united
to each other in varying proportions, still the
carbon, oxygen, hydrogen, and nitrogen, which
surround or penetrate the living animal, are
never directly built up into these tissues. On
the contrary, the various substances which
form the proximate principles of the several
structures of the organism are themselves
produced by the metamorphosis of kindred
compounds introduced in the food ; com-
pounds which have been in their turn derived
from the vegetable kingdom ; either directly,
in the shape of plants, or indirectly, from sub-
stances constructed out of" vegetable tissues
by the organism of another animal. And the
inorganic substances introduced into the body
seem to be almost restricted to the subordinate
(though equally indispensable) office, of com-
bining with these products of vegetable life,
and modifying their actions in obedience to
the necessities of the existing individual.
The above statement as to the organic
nature of the food suggests some interesting
considerations.
In the first place, it seems to shew that
the living animal of to-day pre-supposes
STOMACH AND INTESTINE.
383
another organization of yesterday ; that its
individual descent from two creatures of the
same species is accompanied by a less evident,
but quite as real, transmission of substance
from several previous beings. In short, that
the greater part of its entire mass, might be
regarded as the sum of various legacies, whieh
have been bequeathed to the existing organism
by the various plants and animals that lived
before it.
In the next place, it indicates a fixed and
definite relation between the plant and the
animal. The former is thus the chief agent
in the constructive chemistry of the latter ;
a necessary link in that chain of processes
which builds up organic principles, out of the
elements of inorganic nature, or out of those
simple products into which the particles of the
animal body are finally converted by its waste
during life, or its putrefaction after death.
The carbonic acid given off by the living
or dead animal may especially exemplify the
latter remark ; converted as it is, by the
vegetable, from a poisonous gas into a class
of substances which are in the highest sense
alimentary, and essential to the life of the
animal.
And lastly, since animal and vegetable life
are thus complementary to each other, alike
in their broader features and their minuter
details, we may conjecture that, in the
present disposition of our planet, they form
what is in fact a tolerably constant magni-
tude : a sum of organized life, the amount
of which is subject to but very slight varia-
tion from one time to another. Nay more,
we may almost suspect that the total of
animal existence the composition of which
ranges thus regularly through vegetable or-
ganization as an essential part of its cycle
of metamorphosis is in the main equally
constant and fixed. Created by what even
modern science must be content to own as a
miracle, in the strictest sense of the word, it
seems not improbable that animal, as well as
vegetable life, is sustained in consonance with
some vast law of this kind. According to
such a law, each by each, and both together,
would make up certain constant units ; the
innumerable constituent fractions of which
might vary within vast limits without ex-
ercising any effect on their respective sums.
And thus the world of life around us would
but parallel that perpetual flux, but un-
altered quantity, which the chemist has long
predicated of the various materials which
compose the inorganic globe we inhabit.
But if, on the one hand, the animal is in-
capable of constructing its complex tissues
from the simple elements of inorganic nature,
still, on the other hand, it is not bound down
by such rigorous chemical necessities, as to
demand a food possessing an exact identity
of composition with itself. A large propor-
tion of the animal creation feed on a vegetable
diet, the constituents of which deviate con-
siderably from those of their own mass. And
but very few of even the more carnivorous
animals are in the habit of devouring their own
species. Finally, though the blood forms the
pabulum of all the tissues, and hence closely
approaches their total composition, still it
does not appear to form even an advantageous
article of food, far less an indispensable one.
And while such considerations may suf-
fice to show, that there is no true identity be-
tween the food and the tissues in general, the
progress of modern physiological chemistry