Jones Quain.

Quain's Elements of anatomy (Volume 3:4) online

. (page 13 of 44)
Online LibraryJones QuainQuain's Elements of anatomy (Volume 3:4) → online text (page 13 of 44)
Font size
QR-code for this ebook

plexuses within the salivary glands and pancreas (Drasch, Cajal). According to
Berkeley the nerves end both between the muscular fibres and within the villi by
small pear-shaped or globular dilatations.



DUODENUM. This is the shortest and widest part of the small intestine. In
length it measures about 10 to 12 inches (250 to 300 mm.), and in diameter from
one-and-a-half to two inches (35 to 50 mm.). In its course it describes a single large
curve, which, when the stomach is empty, forms an almost complete ring, its termina-
tion in the jejunum being only a little to the left of its commencement (Braune).
Distension of the stomach, and the consequent movement of the pylorus towards the
right side, makes the curve of the duodenum U -shaped rather than annular. The
curve of the duodenum lies in a coronal plane, except at its two extremities which
are directed forwards. The concavity embraces the head of the pancreas.

It has no mesentery, and is covered only partially by peritoneum. Its muscular
coat is comparatively thick, and its submucous layer towards the pylorus is the seat
of the glands of Brunner, already described. The common bile duct and the
pancreatic duct open into this part of the intestinal canal.

The duodenum may be divided, for the purpose of anatomical description, into
four parts.

The first or superior portion is the most variable part, as its length and direction
depend upon the position of the pylorus. When the stomach is empty it is fully
two inches long, and extends from the pylorus to the right in contact with the
quadrate lobe of the liver, and then backwards beneath the neck of the gall-bladder,
where it bends sharply downwards to join the second part. If the stomach be fully
distended, the commencement of the first part of the duodenum is moved towards
the right side, while its termination remains stationary, so that its direction is then
almost directly backwards, while its length is diminished to an inch, or even less.
Its anterior surface is covered entirely by peritoneum, but its posterior aspect only
in the neighbourhood of the pylorus.



Above and in front of it are the liver and gall-bladder. Its close relation to the
latter is indicated by the fact that it is often stained by the exudation of_bile a few
hours after death. Behind it are the portal vein, the gastro-duodenal artery, and
the common bile-duct. The neck of the pancreas lies behind and to its inner side.

The second or descending portion is about three inches long. It commences
just below the neck of the gall-bladder, opposite tht right side of the first lumbar

17 JLG Id'



A, inferior surface of liver ; B, right kidney ; C, C', right and left suprarenal capsules ; D, left
kidney ; E, pancreas ; F, upper part of stomach ; G, spleen ; H, duodenum with a, b, c, d, its four
portions ; I, jejunum ; K, duodeno-jejunal junction ; 1, lower end of oesophagus ; 2, pyloric orifice ;
3, cceliac axis ; 4, coronary artery ; 5, hepatic artery ; 6, lobus Spigelii of liver ; 7, 7', splenic vessels ;

vertebra, and passes down to the level of the body of the third or fourth lumbar
vertebra, where it turns sharply inwards to join the third part. Its anterior surface
usually gives attachment to the transverse meso-colon, and is entirely covered by
peritoneum, with the exception of the small interval between the two layers of the
meso-colon. This small uncovered area is sometimes considerably increased, owing
to the transverse colon being here destitute of a meso-colon, and separated from the
duodenum by areolar tissue only. Above the transverse colon the anterior surface is
in contact with the liver. The posterior surface has no peritoneal covering, but is
connected by areolar tissue to the right kidney and its vessels and the inferior vena


cava. There are considerable variations in the relations of the second part of the
duodenum to the right kidney. According to Cunningham, they are probably
due rather to variations in the position of the kidney than of the duodenum.
As a rule, the duodenum comes in contact with the kidney a little above
its hilum, and reaches down to about the level of its lower end. To the
left is the head of the pancreas (see fig. 131), which adapts itself to the shape of
the intestine on that side, and, according to Verson, some of the longitudinal fibres
of the gut are intercalated amongst the contiguous lobes of the gland. The common
bile-duct descends behind the left border of this part of the duodenum, and the
pancreatic duct accompanies it for a short distance. On opening into this part of
the duodenum, the valvulae conniventes appear numerously, and a downwardly
projecting papillary eminence of the mucous membrane is found immediately below
one of these, about four inches from the pylorus, on the inner and back part of the
intestine, at the apex of which is seen the common orifice of the biliary and
pancreatic ducts.

The third or transverse portion of the duodenum is between two and three
inches long. Beginning on the right of the third or fourth lumbar vertebra, it
crosses over to the left side, with a slight upward inclination, and ends to the
left of the aorta by curving upwards to join the ascending or terminal part
of the duodenum. Its anterior surface is covered by peritoneum at its commence-
ment, but near the median plane it becomes separated from the anterior layer of
the mesentery by the superior niesenteric vessels which groove its anterior surface.
Behind, it lies against the inferior vena cava and the aorta. On the right side its
posterior surface is uncovered by peritoneum, but towards the left the posterior layer
of the mesentery is prolonged upwards behind it for a variable distance. Above it
is the head of the pancreas.

The fourth or ascending portion (Treves) is about two inches long. It passes
upwards on the left side of the aorta as high as the upper border of the second
lumbar vertebra, where it turns abruptly forwards to join the jejunum, forming the
duodeno-jejunal flexure. It is covered in front and on the left side by the peritoneum,
which often forms on its left side one or two peritoneal pouches called the duodeno-
jejunal fossae, and it lies immediately behind the transverse meso-colon, which
separates it from the stomach. It rests on the left psoas muscle, the inner edge of
the left kidney is sometimes slightly overlapped by it, and near its upper end the
left renal vein passes behind it.

The upper end of this part of the duodenum is maintained in position by a
strong fibrous band descending from the left crus of the diaphragm, and the tissue
around the coeliac axis. This band, which is better marked in the foetus and young
child than in the adult, contains plain muscular fibres, and is called the musctdus
suspensorius duodeni. In subjects in which the intestines are large and dilated
the curve of the duodenum may descend to the level of the iliac crest, but, owing
to the support given by the band alluded to, its terminal extremity maintains a
nearly uniform position.

As a rule, the second, third and fourth parts of the duodenum together form a
U-shaped bend, with the concavity looking upwards, but occasionally the third part
passes across the front of the vertebral column, with a considerable degree of
obliquity, giving rise to the V-shaped type of duodenal curve. In these cases the
distinction between the third and fourth parts is not well marked.

Jejunum and Ileum. The jejunum, originally so called from its having
been supposed to be empty after death, follows the duodenum, and includes the
upper two-fifths of the remainder of the small intestine, while the succeeding three-
fifths constitute the ileum, so named from its numerous coils and convolutions.
Both the jejunum and the ileum are attached to the posterior abdominal wall by an



extensive fold of peritoneum termed the mesentery. This mesentery, although
greatly frilled out in front to correspond in length with the jejunum and ileum
to which it gives support, is attached posteriorly by a comparatively short border
(about six inches), which extends from the left side of the second lumbar vertebra
obliquely across the third part of the duodenum, aorta, inferior vena cava, and right
psoas muscle to the right iliac fossa, where it ends. The length of the mesentery,
measured from the parietal attachment to the intestine, varies, being longer about
the middle than at either end of the bowel. The average length, according to
Treves, may be taken as eight to nine inches. Lockwood found that up to the age
of forty years it rarely exceeded eight inches, but after this period of life longer
mesenteries occurred with greater frequency. Between the two layers of the
peritoneum forming the mesentery are placed, besides some fat, numerous branches
of the superior mesenteric artery and vein, together with nerves, lacteal vessels, and
lymphatic glands. The convolutions of the jejunum and iieum occupy parts of the
middle and lower zones of the abdomen, and a variable number of loops lie in the
pelvis. The jejunum lies above and to the left of the ileum, but the coils are so
irregular that the. position of any individual loop aifords but little clue to the part
of the intestine to which it belongs. The terminal portion of the ileum is more
fixed in position than the other parts of the jejuno-ileum. It generally passes
outwards and upwards from the cavity of the true pelvis across the right psoas
muscle to join the large intestine, being united to the psoas by the lower part of
the mesentery, which here is usually very short.

The character of the intestine gradually changes from its upper to its lower end,
so that portions of the jejunum and ileum, remote from each other, present certain
well-marked differences of structure. Thus, the ileum is narrower ; its coats are
thinner and paler ; the valvulae conniventes are small, and gradually disappear towards
its lower end ; the villi are shorter ; and the groups of Peyer's glands are larger and
more numerous. The diameter of the jejunum is about one inch and a half, that of
the ileum about one inch and a quarter. A given length of the jejunum weighs
more than the same of the ileum.

Meckel's diverticulum. In about one in fifty subjects a pouch or diverticulum
is given off from the main tube of the ileum. Its average position above the ileo-
colic opening is about 43 inches, but it has been found to vary from 11 to 120
inches. It usually comes off from the ileum on the side opposite to the attachment
of the mesentery. As a rule, it is from two to three inches in length, and about the
same calibre as the bowel from which it arises. The origin of this diverticulum is
probably connected with the persistence of a part of the vitelline duct of early foetal
life. It is not to be confounded with hernial protrusions of the mucous membrane,
which may occur at any point.

Variations with ag-e and sex. Treves found the average length of the small intestine
in the new-born child to be 9 feet 5 inches, and he estimates that it grows about 2 feet during
the first month of extra-Uterine life and a similar amount in the second month, but after this
period its rate of growth is very variable. Treves gives the average length of the small
intestine in the adult female as 10 inches longer than that of the male ; but Rolssen, from
measurements on German subjects, found it about 2 feet longer in the male.


The large intestine extends from the termination of the ileum to the anus.
It is divided into the ccecum (with the vermiform appendix), the colon and the
rectum ; and the colon is again subdivided, according to its direction, into four
parts, called the ascending, transverse, and descending colon, and the sigmoid colon
or flexure.



The length of the large intestine is usually about 5 or 6 feet ; being about one-
fifth of the whole length of the intestinal canal. Its diameter, which for the most
part greatly exceeds that of the small intestine, varies at different points and under
different conditions, from 2| inches to less than an inch. It diminishes gradually


(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, fundus of gall-bladder ; 7, cardia of stomach ; 8, funclus
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.

from its commencement at the caecum to its termination at the anus, excepting that
there is a well-marked dilatation of the rectum just above its lower end.



In outward form, the greater part of the large intestine differs remarkably from
the small intestine ; for, instead of constituting an even cylindrical tube, its surface
is thrown into numerous sacculi, marked off from each other by intervening constric-

Fig. 133. TRANSVERSE COLON, EMPTY AND CONTRACTED. (Drawn by G. C. K. Harbinson. )
a, inferior longitudinal band ; 7>, one of the s.iccules ; c, appendices cpiploicae.

tions, and arranged in three longitudinal rows which are separated by three strong
flat bands of longitudinal muscular fibres (fig. 133). It can also be distinguished
by its appendices epiploicse (see below), which are not found in connection with the
small intestine.


The large intestine has four coats, like those of the stomach and small intestine,
namely, the serous, muscular, snbrnucous, and mucous.


ASCENDING COLON (Allen Thomson), f

s, serous covering ; s', s', reflection of this at the
attached border forming a short wide mesocolon between
the folds of which the blood-vessels are seen passing to
the colon ; a, one of the appendices epiploicae hanging
from the inner border ; I in, indicates at the free border
one of the three bands formed by the thickening of the
longitudinal muscular coat ; the dotted line continued
from the margins of these bands represents the remainder
of the longitudinal muscular coat, and the thick line
within it, marked c m, represents the circular muscular
layer ; m, the mucous membrane at the flattened part ;
r, the crescentic bands or indentations which divide the

The serous coat is for the most part
similar to that of the small intestine, except
that, along the colon and upper part of the
rectum, it is prolonged into numerous little
projections, which enclose a certain amount of fat, and are termed appendices



lumen of

goblet cell.

The muscular coat, like that of the other parts of the intestinal canal, consists
of external longitudinal and internal circular fibres.

The longitudinal fibres, although found in a certain amount all round the intes-
tine, are, in the cnecum and colon, more thickly collected into three remarkable flat
longitudinal bands (fig. 134, Im ; fig. 133, a). These bands, sometimes called the
ligaments of the colon, are about 12 mm. wide, and 1 mm. thick ; they commence
upon the csecum, at the attachment of the vermiform appendix, and may be traced
along the whole length of the colon as far as the commencement of the rectum,
where they form the two bundles which pass down, one on its anterior and the
other on its posterior surface. One of these bands, the posterior, is placed
along the attached border of the intestine ; another runs along its anterior

epithelium. Fig. 135. SECTION OP THE MUCOUS MEM-


and v. Davidoff. ) ^OL

border, and, in the transverse
colon, corresponds with the
attachment of the great omen-
turn ; whilst the third band (inner
or inferior) is found on the inner
border of the ascending and
descending colon, and on the
under border of the transverse
colon. It is near the course
of this third band that the
appendices epiploica? are most of
them attached (fig. 134, a).
Measured from end to end, these
three bands are shorter than the
intervening parts of the tube ;
and the latter are thus thrown
into the succuli already men-
tioned : accordingly, when the
bands are removed by dissection,
the sacculi are entirely effaced,
and the colon, elongating con-
siderably, assumes the cylindrical
form. The transverse constric-
tions seen on the exterior of the
intestine, between the sacculi,

appear on the inside as sharp ridges separating the cells, and are composed of all

the coats. In the vermiform appendix the longitudinal muscular fibres are disposed

in a uniform layer.

The circular muscular fibres form only a thin layer over the general surface of

the caecum and colon, but are accumulated in large numbers between the sacculi.

In the rectum, especially towards its lower part, the circular fibres form a very thick

and powerful muscular layer.

The submucous or areolar coat resembles in all respects that of the small


The mucous membrane differs from that of the small intestine in being smooth

and destitute of villi. Viewed with a lens, its surface is seen to be marked all over

by the orifices of numerous tubular glands (crypts of Lieberkiihri) (fig. 135), resembling

those of the small intestine, but longer and more numerous, and further distinguished

in terglandu Jar

areolar tissue
of mu coiis



from them by the large number of mucus-cells which they contain. Indeed in
some animals all the cells of these glands may be found to be filled^ with mucus

Fig. 136. GLANDS OF THE LARGE INTESTINE. MAGNIFIED (from Heidenhain and Klose).
a, of the rabbit ; 6, of the dog. c, transverse section of a gland of the dog.


of surface.

lymphoid cells


area of multi-
plication of
lymphoid cells.


(Bb'hm and v. Davidoff.)

(fig. 136, a) ; in others every alternate cell presents this character (fig. 136, 5, c), the
cells between being of the ordinary columnar kind. If the glands are stimulated



to active secretion the mucus is discharged and all the cells nssume the appearance
of ordinary columnar epithelium-cells (Klose).

Scattered over the whole large intestine lymphoid nodules are found, similar to
the solitary glands of the small intestine. They are most numerous in the csecum
and its vermiform appendix ; being placed closely all over the latter.

The epithelium which covers the general surface of the mucous membrane is of


a, artery passing up from submucosa ; c, vein arising from
capillary plexus, b, which surrounds the mouths of the glands.

the columnar kind, and in every respect similar to
that of the small intestine. As in the stomach the
mucous membrane consists of areolar connective
tissue with a certain amount of retiform tissue, and is
bounded next the submucous coat by a layer of plain
muscular fibres (muscularis mucosce), which sends
prolongations up between the glands to be attached
to the basement membrane near the surface, in the
same way as in the villi of the small intestine.

Vessels and Nerves. In the large intestine
an arrangement of capillary plexuses and venous
radicles obtains, similar to that which has been
described in the stomach (fig. 138). The arrange-
ment of the lymphatics is also nearly the same.

Nervous plexuses similar to those of the small intestine are also found in the
muscular and submucous coats of the large intestine.


THE CJECUM. The intestinum ccecum, or caput ccvcum coli, is that part of the large
intestine which is situated below the entrance of the ileum (fig. 132, 11). Its
length is about 2| inches, and its breadth about three inches ; it is the widest part
of the large intestine.

The caecum is situated in the right iliac fossa, in front of the ilio-psoas muscle
and immediately behind the anterior wall of the abdomen above the outer half
of Poupart's ligament. It is covered by the peritoneum in front, below and at
the sides ; behind, the peritoneum is usually reflected from the bowel on to the
iliac fascia at the level of the ileo-colic opening, or even still higher up, so that
the posterior surface is entirely invested. In about 5 p.c., however, the reflection
occurs at a lower level, in which cases the upper part of the posterior surface
is uncovered and connected with the iliac fascia by areolar tissue. There is no

In the fostus the caecum is conical in form, and its apex gives attachment to a
slender process called the vermiform appendix. The three longitudinal bands of the
large intestine are united at the root of the appendix, but on the caecum they diverge,
one passing up the anterior surface, another on the inner side, and a third on the
postero-external aspect. This, the infantile type of caecum, may persist in the adult,
Treves found it in two out of one hundred adult subjects. In the great majority of
cases, however, the walls of the caecum begin, even before birth, to grow at unequal
rates. The anterior and right walls grow more rapidly than the posterior and left
ones, so that the attachment of the vermiform appendix is no longer situated at the



lower end, but is found on the inner and posterior aspect of the caecum. The three
bands, however, are still found to unite at the root of the appendix. The free,
rounded and usually blunt lower end of the caecum thus comes to be formed by the
expanded saccule situated between the anterior and postero- external bands. In the
third month of foetal life the caecum is situated near the median plane just below the
liver, and in the process of development it normally passes downwards and to the
right, in front of the second part of the duodenum and the kidney towards the right
iliac fossa. In the 6th month it lies opposite the lower end of the kidney, and at birth
it has usually attained its adult position. This process of descent of the caecum is
liable to be arrested in any part of its course. On the other hand the cascum is
sometimes unusually long and movable, and its free extremity may project down into
the true pelvis or even pass across the median plane to the left side. It has been




(Drawn by G. C. R.

a, lower end of ileum ;
b, its mesentery ; c, c, caecum ;
(/, orifice of vermiform appen-
dix ; e, ileo-colic orifice ; /,
upper or ileo-colic segment of
its valve ; g, lower or ileo-
ceecal segment ; h, ascending

0- \

found rotated on its
long axis so that the
ileum, after passing be-
hind the caecum, opened
on its right side.

Coming off from the
inner and back part of
the caecum, a little below
the ileo-colic opening is
a narrow, round, and
tapering portion of the
intestine, named the
appendix cwci, or vermi-
form appendix. The width of this process is usually about 6 mm., and its
average length 92 mm. (Berry), but it varies considerably ; thus, Berry found
it, in two out of 100 cases, only 31 mm. in length, and Ransshoff has recorded
one 230 mm. long. It varies considerably in its position, but will generally be
found passing from behind the caacum either upwards and to the left behind
the ileum and mesentery in the direction of the spleen (Treves), or downwards
and to the left so as to lie on the brim of the pelvis or even project into that
cavity. Sometimes it is situated entirely behind the caecum, and in this posi-

Online LibraryJones QuainQuain's Elements of anatomy (Volume 3:4) → online text (page 13 of 44)