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the cell clear of granules (fig. 95). After digestion has ceased the outer parts of the cells
become again partially or wholly occupied by granules (Langley). On the other hand the
parietal cells of the cardiac glands are smaller during fasting, and are then angular in form
(fig. 98). During digestion, on the other hand, they become enlarged and more spheroidal,
bulging out the tunica propria of the glands (fig. 99).

Heidenhain first showed that both the central cells and the parietal cells undergo a change
of size during digestion, becoming at first enlarged and subsequently shrinking to less than
their volume during rest. The changes occur later in the parietal than in the central cells.

The secreting cells of the pyloric glands undergo changes which are similar to those of the
central cells of the cardiac glands (Ebstein).

Between the glands and at their base the mucous membrane consists of delicate
connective tissue with retiform lymphoid tissue in small amount.

A thin layer of plain muscular tissue (muscularis mucosce, fig. 91, m.m.) bounds

Fig. 100. SECTION THROUGH THE

COATS OF THE STOMACH TO




SHOW THE ARRANGEMENT OF

THE

SELS.



PRINCIPAL BLOOD-VKS-

(Mall.)

On the right side of the figure
the glandular and muscular ele-
ments are shown ; on the left only
the blood-vessels. It will be seen
that the principal vessels are in
the submucous tissue, and that
from these, branches are distrib-
uted to the mucous membrane and
to the muscular coat.

the mucous membrane ex-
ternally, separating it from
the submucous tissue. It
consists of more than one
stratum (an outer longitu-
dinal and an inner circular),
and is better marked in
some animals than in man.
Offsets pass from it between
the gastric glands towards
the surface of the mucous
membrane.

Lymphoid Follicles.
The stomachs of young
persons sometimes present
a mamillated aspect, due
to little elevations of the
surface, which are pro-
duced by local accumula-
tions of lymphoid tissue, and somewhat resemble the solitary follicles of the
intestine in appearance. The lymphoid accumulations in question are situated
amongst the glands, and do not extend into the submucous tissue ; they are
not so distinctly circumscribed as those of the intestine, but fade off into the
surrounding retiform tissue. They are most numerous near the junction of the
stomach and small intestine (Watney). They vary in development in different
individuals, and are sometimes not to be found at all.

Vessels and Nerves. The stomach is a highly vascular organ. Its arterial
branches, derived from all three divisions of the codiac axis, reach the stomach



THE STOMACH,



between the folds of the peritoneum, and form, by anastomosing together, two
principal arterial arches, which are placed along its two curvatures. Their branches
pass through the muscular coat (to which in passing they give off some arterioles)
and divide into smaller vessels in the submucous areolar tunic, where they also
freely anastomose, and whence they are distributed to the mucous membrane and to
the muscular layers. The arterial branches (fig. 101, a) which enter the mucous
membrane, pass between the tubuli, ramifying freely in a radial manner ; here
they form a plexus (d) of fine capillaries upon the walls of the tubules ; and from
this plexus larger vessels pass into a coarser capillary network around the mouths of
the glands. The veins, fewer in number than the arteries, arise from the latter
network, and take an almost straight course (c, c) through the mucous membrane
between the glands and join to form a plexus of larger vessels near the bases of the
glands. From this plexus branches pass off, which, after piercing the muscularis
mucosas and forming a wide venous plexus in the submucous tissue, return the





Fig. 101. PLAN OP THE BLOOD-VESJELS OF THE MUCOUS MEMBRANE OF THE STOMACH.
(Modified from Brinton. )

a, small arteries passing to break up into the fine capillary network, d, between the glands ; b,
coarser capillary network around the mouths of the glands ; c, c, veins passing vertically downwards
from the superficial network ; e, larger vessels in the submucosa.

Fig. 102. LYMPHATICS OF THE HUMAN GASTRIC MUCOUS MEMBRANE, INJECTED (from Loven).

The tubules are only faintly indicated ; a, muscularis mucosae ; b, plexus of fine vessels at base of
glands ; c, plexus of larger valved lymphatics in submucosa.

residual blood into the splenic and superior mesenteric veins, and also directly
into the vena porta?. These veins, as well as other tributaries of the vena porta,
have a particularly Nvell-marked muscular coat, and contain numerous valves
(Hochstetter).

The lymphatics are very numerous. As shown by Loven, they arise in the
mucous membrane (fig. 102) by a dense network of lacunar spaces, situated between
and amongst the gland-tubuli, which, as well as the blood-vessels, in many parts
they enclose in sinus-like dilatations. Near the surface of the membrane the lymph
is collected into vessels which form loops or possess dilated extremities : these
vessels are less superficial than the blood capillaries. At the deeper part of the
mucous membrane the interglandular lymphatics pass into a plexus of fine
vessels (b), immediately underlying the tubular glands ; then piercing the
muscularis mucosse (a), they form a coarser, more deeply-seated network (c) in the

o 2



84



ORGANS OF DIGESTION.




submiicous' coat, the vessels of this network being provided with valves. Thence
efferent lymphatics proceed, and, piercing the muscular coats, follow the direction of
the blood-vessels beneath the peritoneal investment, and traverse lymphatic glands
found along the two curvatures of the stomach.

The turves, which are large, consist of the terminal branches of the two pneumo-
gastric nerves, belonging to the cerebro-spinal system, and of offsets from the
sympathetic system, derived from the solar plexus. The left pneumo-gastric nerve

Fig. 103. VIEW OF THE PYLORUS AND DUODENUM FROM

BEFORE. THE STOMACH AND DUODENUM HAVE BEEN
DISTENDED AND HARDENED IN SPIRIT, AND THE GREATER
PART OF THE STOMACH THEN CUT AWAY. (Slightly

altered from Luschka.) ^

12, the twelfth dorsal vertebra and rib ; 1, 3, 4, 5, trans-
verse processes of the first, third, fourth, and fifth left lumbar
vertebrae ; 2, that of the second on the right side ; a, a, the
abdominal aorta above the cceliac axis and also near the
bifurcation ; m, superior mesenteric artery ; v, v, the vena
cava above the renal veins and near the bifurcation ; p, placed
on the first part of the duodenum, points to the pyloric
orifice seen from the side next the stomach, of which a small
part is left connected with the intestine ; d, on the descend-
ing part of the duodenum, indicates the termination of the
common bile-duct and the pancreatic duct ; d', the ascending
part of the duodenum ; j, the commencement of the jejunum.
(This is represented as drawn over to the left, instead of
curving forward, as is actually the case.)

descends on the front, and the right upon the back of the stomach, and both
nerves are here composed almost entirely of non-medullated nerve-fibres. Numerous
small ganglia have been found by Remak and others on both the pneumo-gastric and
sympathetic twigs. The nerves form gangliated plexuses (like the plexuses of
Auerbach and Meissner) of the intestine, both between the layers of the muscular
coat and in the submucous coat. From these plexuses nerve-fibrils proceed to the
muscular tissue and to the mucous membrane.

The Pylorus. While there is no special apparatus at the cardiac orifice of the
stomach for closing the passage from the oesophagus, the opening at the pyloric

Fig. 104. SECTION THROUGH PYLORIC PART OF

STOMACH AND COMMENCEMENT OF DUODENUM,
FROM A SPECIMEN HARDENED IN SITU. (J. S. ) j

a, a, a, longitudinal folds of the mucous mem-
brane in pyloric part of stomach ; 6, section of
mucous membrane ; c, circular muscular fibres of
stomach : the longitudinal fibres are just visible to
the naked eye as a narrow line external to the
circular fibres ; D, duodenum ; p, pyloric orifice.

end, leading from the stomach into the
duodenum, is provided with a sphincter
muscle. On looking into the pyloric end

of a distended stomach, the mucous membrane is seen projecting in the form
of a circular fold, called the pylorus, leaving a correspondingly narrow opening.
Within this fold are circular muscular fibres, belonging to the general system
of circular fibres of the alimentary canal, which are here collected in the form of
a strong band, whilst the longitudinal muscular fibres and the peritoneal coat
pass over the pyloric fold to the duodenum, and do not enter into the forma-
tion of the sphincter (fig. 104, p ; fig. 105). Externally the pylorus may be
easily felt, like a thickened ring, at the right end of the stomach, where also a




THE STOMACH.



85




slight external constriction is visible. Internally its opening is usually circular,
and even when the stomach is artificially distended after death it measures Less than

Fig. 105. DIAGRAMMATIC VIEW IN PERSPECTIVE OF A PORTION

OF THE COATS OF THE STOMACH AND DUODENUM, INCLUDING

THE PYLORUS. (Allen Thomson. )

ff, the inner surface of the gastric mucous membrane ; g',
section of the mucous membrane with the pyloric gastric
iilands ; ?', the villous surface of the mucous membrane of
the duodenum ; i. section of the same with the intestinal
glands or crypts of Lieberkiihn ; p p, the ridge of the pyloric
ring, with a section of its component parts ; mi, deep or cir-
cular layer of muscular fibres : these are seen in the section to

form the pyloric sphincter ; me, external or longitudinal layer of muscular fibres ; s, the serous
covering.

half an inch (12 mm.) across, so that it is the narrowest part of the whole alimentary
canal.

Occasionally the orifice is oval, and it is often placed a little to one side.
Sometimes the circular rim is imperfect, and there are found instead two crescentk'
folds, placed one above and the other below the passage (Huschke) ; and, lastly,
there is occasionally but one such crescentic fold.

When the sphincter is contracted the longitudinal fibres covering it are bowed
inwards, and these, if they contract at the same time that the sphincter muscle
relaxes, will tend to dilate the orifice.



BECENT LITERATURE OF THE STOMACH.

Aufschnaiter, O., Die Muskelhaut d. menschl. Magens, Sitzungsb. d. Wiener Akad., Bd. ciii,
1894.

Bizzozero, GK, Ucber die schlauchformigen Drusen des Magendarmkanals und die Beziehungen
ihres Epithels zu dem Oberfldchenepithel der Schleimhaut, Archiv f. mikroskop. Anat., Bd. xxxiii,
1889 ; Bd. xl, 1892; and Bd. xlii, 1893.

Capparelli, Andrea, Die nervosen Endigungen in der Magenschleimhaut, Biolog. Centralbl.,
1891.

Contejean, Ch., Sur les fonctions des cellules dcs glandes gastriques, Archives de physiol.
normale et patholog., 1892.

Golgi, C., Sur la fine organisation des glandes peptiques des mammiferes, Arch, italiennes de
biologic, t. xxi, 1893.

G-ubaroff, A. v., Ueber den Verschluss des menschlichen Magens an der Cardia, Archiv f.
Anatom. u. Physiol., Anatom. Abt., Jahrg. 1886.

Hamburger, Ernst, Bcitrdge zur Kenntniss der Zellen in den Magendrusen, Archiv fur
mikroskop. Anat., Bd. xxxiv, 1889.

Langendorff, O. , und Laser stein, S., Die feineren Absonderungsweye der Magendrusen,
Arch. f. d. ges. Physiol., Bd. Iv, 1894.

Lesshaft , P. , Veber die Lo,ge des Magens und ueber die Beziehungen seiner Form und seiner
Function, Arch. f. pathol. Anat., 1882.

Martins, F. , Ueber Grosse, Lage u. Beweglichkeit d. gesunden u. kranken menschl. Magens,
Wiener med. Blatter, xvii, 1894.

Muller, E., Zur Kenntniss der Labdrusen der Magenschleimhaut, Biolog. Forens. Forhandl.,
Stockholm. 189192, Jahrg. iv.

v. Openchowski, Th., Ueber die gesammte Innervation des Magens, Deutsche medicin.
Wochensch., 1889.

Ost, A., Beitrcige zur Bestimmufig der Capacitdt des Magens, Diss., Dorpat, 1891.

Pilliet, A., Sur I'evolution des cellules glandulaires de I'estomao chez Vhomme it les vertebres,
Journal de 1'anatomie, 1887.

Keynier et Souligroux, Direction de Vestomac, Bull. soc. anat., Paris, 1891.

Schmidt, M., Zu der Anatomic des Magens am Lebenden und der Diagnose der Dilatatio
vcntriculi, Berliner klinische Wochenschrift, Jahrg. xiii, 1886.

Stein, C., Ueber das Vcrhalten des Bindegewebes zu den dclomorphen Zellen der Magendrusen t
Mitteil. aus d. embryol. Instit. der Uuiversitat Wien, 1892.

Windle, B. C. A., On the sacculation of the human stomach, Proc. of the Birmingham Philosoph.
Soc., vol. v, 1886.



86 ORGANS OF DIGESTION.



THE SMALL INTESTINE.

The small intestine commences at the pylorus, and, after many convolutions,
terminates in the large intestine. It measures, on an average, about 22 feet in
length in the adult, and becomes gradually narrower from its upper to its lower end.
Its convolutions occupy the middle and lower parts of the abdomen, and also
frequently descend into the pelvis.

The small intestine is divided into three portions, which have received different
names. The first ten or twelve inches immediately succeeding to the stomach, and
comprising the widest and most fixed part of the tube, is called the duodenum.
This part is further distinguished by its close relation to the head of the pancreas,
and by the absence of a mesentery. The remainder, which is arbitrarily divided
into an upper two-fifths called the jejunum, and a lower three-fifths called the ikum, is
very convoluted and movable, being connected with the posterior abdominal wall by
a long and extensive fold of peritoneum called the mesentery, and by numerous
blood-vessels and nerves. Although there is no distinct line of demarcation between
the jejunum and the ileura, yet the portion of the small intestine included under
these two names gradually undergoes certain changes in structure and appearance
from above downwards, so that the upper end of the jejunum can readily be
distinguished from the lower part of the ileum.



STRUCTURE OF THE SMALL INTESTINE.

The small intestine, like the stomach, is composed of four coats, viz., the serous
or peritoneal, muscular, areolar, and mucous.

The external or serous coat almost entirely surrounds the intestinal tube in the
whole extent of the jejunum and ileum, leaving only a narrow interval behind,
where it passes off and becomes continuous with the two layers of the mesentery.
The line at which this takes place is named the attached or mesenteric border of the
intestine. The duodenum, on the other hand, is but partially covered by the
peritoneum.

The muscular coat consists of two layers of fibres ; an outer longitudinal, and
an inner or circular set. The longitudinal fibres constitute an entire but com-
paratively thin layer, and are most obvious along the free border of the intestine.
The circular layer is thicker and more distinct.

The muscular tunic becomes gradually thinner towards the lower part of the
small intestine. It is pale in colour, and is composed of plain muscular tissue, the
cells of which are of considerable length. The progressive contraction of these
fibres, commencing in any part of the intestine, and advancing in a downward
direction, produces the peculiar vermicular or peristaltic movement by which the
contents are forced onwards through the canal. In the narrowing of the tube the
circular fibres are mainly concerned, the longitudinal fibres tending to produce
dilatation (Exner) ; and those found along the free border of the intestine may have
the effect of straightening or unfolding its successive convolutions. There is a
gangliated plexus of nerve-fibres and a network of lymphatic vessels between the
two muscular layers.

The submucous coat of the small intestine is a layer of areolar tissue of a
loose texture, which is connected more firmly with the mucous than with the
muscular coat. "Within it the blood-vessels ramify before passing to the mucous
membrane, and there is a gangliated plexus of nerve-fibres and a network of large
lymphatic vessels.



THE SMALL INTESTINE.



s?



The internal coat or mucous membrane is characterised by the finely flocculent or
shaggy appearance of its inner surface, resembling the pile upon velvet.. This appear-




18



22



Fig. 106. DIAGRAM SHOWING THE POSITION OF THE THORACIC AND ABDOMINAL ORGANS.

(Rauber after Luschka. )

1, Lower border of the right lung ; 2, the same of the left lung ; 3, liver, right lobe ; 4, liver, left
lobe ; 5, suspensory ligament of the liver ; 6, funclus of gall-bladder ; 7, cardia of stomach ; 8, fundus
of stomach ; 9, lower border of stomach ; 10, position of pylorus ; 11, caecum ; 12, vermiform appendix ;
13, ascending colon; 14, right flexure of colon ; 15, transverse colon; 16, position of left flexure of
colon ; 17, descending colon ; 18. portion of sigmoid colon, concealed by 19, convolutions of the small
intestine ; 20, termination of ileum, ascending from left to right ; 21, bladder, distended, partly
covered by peritoneum ; 22, the part of the bladder which is not covered by peritoneum.



ance is due to the surface being thickly covered with minute processes named villi. It is
one of the most vascular membranes in the body, and is naturally of a reddish



88



ORGANS OF DIGESTION.



colour in the upper part of the small intestine, but is paler, and at the same time
thinner, towards the lower end. It is lined with columnar epithelium throughout
its whole extent, and next to the submucous coat is bounded by a layer of plain
muscular tissue (muscularis mwoscK) ; between this and the epithelium the sub-
stance of the membrane, apart from the tubular glands which will be afterwards
described, consists mainly of retiform tissue which supports the blood-vessels,
nerves, and lymphatics (lacteals), and encloses in its meshes numerous lymph-
corpuscles.

Fig. 107. PORTION OF SMALL INTESTINE DISTENDED

WITH ALCOHOL AND LAID OPEN TO SHOW THE

VALVUL.E CONNIVENTES. (BrintoD.)

Valvulae coniiiveiites. The mucous
membrane, in addition to small effaceable
folds or rugae, possesses also permanent
folds, which cannot be obliterated, even
when the tube is forcibly distended.
These permanent folds are the valvulce,

conniventes or valves ofKerkring. They are crescentic projections of the mucous mem-
brane, placed transversely to the axis of the bowel and following one another closely.
The majority of the folds do not extend more than about one-half or two-thirds
round the interior of the tube, but it has been shown by Brooks aud Kazzander that
some form complete circles, and others spirals. The spiral forms may occur singly
or in groups of two or three. They generally extend a little more than once round
the bowel, but in rare cases may go round two or three times. At their highest
point they project inwards for about a third of an inch. Some of the valvulae
conniventes are bifurcated at one or both ends, and others terminate abruptly.
Each consists of a fold of mucous membrane, that is, of two layers placed back to





Fig. 108. SMALL PORTION OF THE SURFACE OF

THE MUCOUS MEMBRANE OF THE SMALL INTES-
TINE. (Rauber.) -^

1, mouths of nrypts of Liebcrkiihu ; '2, villi.

*? back, and united together by submucous
areolar tissue. They contain no part of
the circular or longitudinal muscular
coats. Being extensions of the mucous
membrane, they serve to increase the
absorbent surface to which the food is
exposed.

The valvulse conniventes are not uniformly distributed over the various parts of
the small intestine. There are none quite at the commencement of the duodenum ;
a short distance from the pylorus they begin to appear ; beyond the point at which
the bile and pancreatic juice are poured into the duodenum they are very
large, regularly crescentic in form, and placed so near to each other that the
intervals between them are not greater than the breadth of one of the valves ; they
continue thus through the rest of the duodenum and along the upper half of the
jejunum ; below that point they begin to get smaller and farther apart, and finally,
towards the middle or lower end of the ileum, having gradually become more
irregular and indistinct, sometimes even acquiring a very oblique direction, they
altogether disappear.

The villi, peculiar to the small intestine, and giving to its internal surface



THE SMALL INTESTINE.



89




epithelium f>f

vittus.



connective tis-
sue of villus.



epithelium of
villus.



f/oblet cell.

crypt of
" Liebcrkiihn.



connective tis-
- . sue at base of
glands.

- ' muscular is
mucosce.



the velvety appearance already
spoken of, are small processes of
the mucous membrane, which
are closely set on every part of

Fig. 109. SECTION OF THE HUMAN
INTESTINAL MUCOUS MEMBRANE
(? CHILD), SHOWING THREE VILLI
WITH CRYPTS OF LlEBERKUHN.
(Bohm and v. Davidoff. ) - 8 -f

the inner surface over the valvulse
conniventes, as well as between
them.

Their length varies from
0'5 mm. to 0'7 mm., or some-
times more. They are largest
and most numerous in the
duodenum and jejunum, and
become gradually smaller, and
fewer in number in the ileum.
According to Rauber, they are
short and leaf-shaped in the
duodenum, and as the gut is
followed downwards they become
gradually longer and thinner, so
that they are tongue-shaped in
the jejunum, and filiform in
the ileum. Occasionally two or
three are connected together at their base. In the upper part of the small
intestine there are from 10 to 18 villi in a square millimeter, and in the ileum from
8 to 14 in the same space. This would give about 4 millions altogether (Krause).

Fig. 110. PART OF A SECTION

THROUGH A VILLUS OF THK
DOG, HIGHLY MAGNIFIED.

(R. Heidenhain.)

m, m, muscular fibres ; I, I', I",
lymph-corpuscles ; bl, blood-ves-
sels ; c, branched connective tissue
corpuscles, covering the reticular
fibres. The epithelium of the villus
is not represented.



Chaput describes the villi
as being so closely arranged as
to be separated merely by
narrow clefts into which the
crypts of Lieberkiihn open.
This may be the case in the
empty condition of the in-
testine, but when it is dis-
tended they are necessarily
more separated from one
another as. usually described.

A villus consists of a
prolongation of the proper
mucous membrane. It is
covered by columnar epi-
thelium (fig. 109), and en-




90



ORGANS OF DIGESTION.



closes a network of blood-vessels, one or more lymphatic vessels (lacteals), and a few
longitudinal plain muscular fibre-cells, these being all supported and held together by
retiform lymphoid tissue. Under the epithelium is a basement membrane composed of
flattened cells, which on the one hand are connected with the branched cells of the
retiform tissue, and on the other hand send processes between the epithelium-cells.
Nervous fibrils penetrate into the villi from the plexus of Meissner, and form arbori-
zations throughout their whole substance (fig. 130, p. 99). Each villus receives, as a
rule, one small arterial twig, which runs from the submucous coat through the mus-

Fig. 111. MAGNIFIED VIEW OF THE

BLOOD-VESSELS OF THE INTESTINAL

VILLI. (Sharpey. )

The drawing was taken from a pre-
paration injected by Lieberkuhn, and
shows, belonging to each villus, a small
artery and vein with the intermediate
capillary network.

" cularis mucosas to the base of the
villus, and then up the centre to
near the middle of the villus,

where it begins to break up into a number of capillaries (fig. 111). These
form near the surface, beneath the epithelium and limiting membrane, a fine
capillary network, from which the blood is returned for the most part by one
or two venules, which in man commence near the tip of the villus, and pass
down to its base to join the venous plexus of the mucous membrane, whence
the blood is conveyed to the large veins of the submucosa. The general
arrangement of the vascular supply of the villi varies considerably in different
animals.

/*




y-



Fig. 112. CROSS SECTION OF A VILLUS OK
THE CAT'S INTESTINE. (Highly magni-
fied.) (E. A. S.)

e, columnar epithelium ; y, goblet cell,
its mucus is seen partly exuded ; Z, lymph -
corpuscles between the epithelium cells ; b,
basement membrane ; c, blood-capillaries ;
m, section of plain muscular fibres ; c.l.,
central lacteal.



The lacteal lies in the centre of
the villus (figs. 112, 113, 114), and
is in the smaller villi usually a single
vessel, with a closed and somewhat
expanded extremity, and of con-
siderably larger diameter than the

capillaries of the blood-vessels around. According to the observations of Teich-



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