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:'''Links:''' [[Book_-_Contributions_to_Embryology|Carnegie Institution of Washington - Contributions to Embryology]] | [[Immune System Development]] | [[Pig Development]]
=On the Development of the Lymphatics in the Stomach of the Embryo Pig=
 
by James R. Cash,
 
From the Anatomical Laboratory, Johns Hopkins University.
 
With three plates and three text-figures.
 
==Introduction==
 
The work of Dr. Mall (1896) on the anatomy of the lymphatics of the wall of the stomach has established the plexiform arrangement of these vessels and their relation to the other structures of this organ. By dissecting the stomachs of dogs in which the lymphatics had been injected, and by reconstructions of such dissections, the entire organ was shown to be supplied with four definite, homogeneous plexuses. The most delicate of these, and the one most intimately related to the lining of the stomach, is the mucosal plexus. It lies in the mucosa at the base of the gastric glands just external to the muscularis mucosse and receives branches which lie between the glands and extend out as far as the gastric pits. Owing to the delicacy of these vessels and the fact that valves prevent their injection from the main plexus of the submucosa, any attempt at complete injection is attended with much difficulty. As a matter of fact, the mucosal vessels can be injected in the adult only by direct puncture, which means that the needle must actually pass through the muscularis mucosa? and enter the narrow zone between it and the base of the gland ; it can be readily seen that such an exact placing of the needle occurs only by chance. However, th( best specimens obtainable indicate clearly that the lymphatics between the glands communicate directly with this delicate, homogeneous plexus lying at the base of the glands of the mucosa.
 
 
Proceeding through the wall of the stomach toward its serous surface, the first
plexus of the submucosa is encountered. This consists of a single layer of lymphatics, just outside the muscularis mucosse, and forms the connecting link between
the mucosal plexus, just described, and the main plexus of the submucosa, the
principal plexus of the wall of the stomach. This main plexus is a dense mass of
vessels which practically fills the submucosa and is composed of several layers of
large, tortuous, thickly arranged lymphatics. Springing from it are numerous
slender vessels which traverse the muscular coats of the stomach, forming a coarse
plexus between them, and are gathered together on the surface of the stomach into
the subserous plexus, a dense, single layer of lymphatics situated just beneath the
peritoneal covering of the organ.
 
 
The work of Dr. Mall extended that of Sappey, Teichmann, and Loven. It
may be seen, therefore, that the anatomy of the lymphatic vessels in the wall of
the adult stomach is well known. The pathways of lymphatic drainage from this
organ, however, are not so clearly understood. All investigations along this line
have consisted in partial injections of the adult stomach. In the present experiments the direction of flow of the injection mass from different points was noted and
from the information so gained the direction of normal lymphatic drainage, in vivo,
is inferred.
 
 
The most extensive work of this kind has been done by Cuneo. By injecting colored substances directly into the main plexus of the submucosa, and watching its the stomach. After Cunoo, 1902.
 
# The coronary or principal current.
# Right gastro-epiploic current.
# Splenic current.
 
 
flow over the wall of the stomach and its appearance in regional lymphatic glands, he
has obtained a very good general idea of this question. As a result, he felt justified
in dividing the stomach into three main lymphatic zones (Poirier and Cuneo, 1902).
These arbitrary zones are shown in text-figure 1. The arrows show the direction
of the flow of lymph from the different parts. Zones 1
and 2 drain the glands of the lesser curvature, while the
flow from zone 3 goes to the hilum of the spleen and
then on to the pre-aortic glands. It is to be noted that
no drainage is indicated by way of the duodenum.
Cuneo states that most of the lymph flows directly
toward the lesser curvature and passes through glands
situated in this region, whose efferent ducts drain into
the pre-aortic lymph-nodes just anterior to the cy sterna
chyli. Zone 1 represents this area. In the area desig-
nated as zone 2 the flow of lymph is toward the pylorus,
as indicated, but passes posterior to it to the glands
of the lesser curvature. From zone 3 lymph passes
through vessels in related folds of peritoneum, to the
hilum of the spleen and from there to the pre-aortic lymph-nodes.
 
TEXT . Fig . 1 ._ Lymphatic tcrritoricn ,
 
 
As one looks at a cross-section of a stomach wall in which the lymphatics have
been injected, the extreme vascularity of the organ becomes immediately apparent.
The plexuses are so dense, permeate the entire organ so thoroughly, and are so rich in
their anastomoses that definite lymphatic zones and fixed points of drainage for the
different regions are anatomically difficult to establish. The more conservative
and apparently more accurate view is that the wall of the stomach contains four
complete lymphatic plexuses, in open communication with each other and through
which lymph may flow, peripherally, in any direction. It is quite difficult to con-
ceive of such dense, homogeneous plexuses being divided into any zone-like arrangement. Certainly, the lymph will leave the stomach by way of the nearest and most
accessible avenue of exit, and injections made around the regions toward which
lymphatic flow occurs will apparently find zones in which most of the flow takes
place in a given direction; but in view of the complex nature of the vessels within
the wall of the stomach the accuracy of areas found in this manner becomes very
doubtful. Thus it is evident that our knowledge of the gastric lymphatics is not yet
complete. Such methods as those mentioned are sufficient only for the formation
of general ideas and beyond this point any statement is speculative. As yet, no
work has been done on the embryology of these vessels. To resolve such dense
lymphatic plexuses into their component parts by injection after they are fully
developed is obviously impractical. By a study of their origin and development it
was hoped that more accurate views might be adopted for the lymphatic drainage
of this organ, and it was with this idea that the present investigations in embryo
pigs were undertaken.
 
 
By the method of injection, embryos can be studied in various stages before
the lymphatic development is complete. In this way the origin of the vessels, the points at which they reach the stomach, their manner of growth, their anastomoses,
and finally the relation of the gastric lymphatics to the lymphatics of other organs
can be observed. Embryos 40, 60, 80, and 120 mm. in length were used. Those
up to 90 mm. were injected through the retroperitoneal sac, or its remains, the
large lymphatic plexus of vessels between the Wolffian bodies. In the embryos
measuring over 90 mm. the injections were made directly into the submucosal
plexus at the lesser curvature, since valves and nodes, forming at this age, prevent
retrograde injection of the organ from the retroperitoneal sac. In such a study it
would be very helpful to have complete injections of the lymphatics of the adult
stomach and its surrounding organs, but the valves and nodes along the course of
the vessels act as effective barriers to extensive injections. For a successful
injection the embryo must be fresh, preferably with the heart still beating. Hypodermic syringes of 1 c. c. capacity with fine needles (No 28), were used for inject-
ing. The best specimens were obtained with a saturated aqueous solution of
Berlin blue as the injection mass. Most of the material was cleared in oil of wintergreen by the Spalteholz method. Thick microscopic sections were cut to show the
progressive development of the plexuses within the stomach wall and the course of
the vessels which traverse the ligaments of the spleen. The actual technique of
injecting the retroperitoneal sac has been described by Baetjer (1908) in his work
on the morphology of that structure and need not be repeated here.
 
 
In their development the lymphatics of the stomach pass to it by way of its related folds of peritoneum. Therefore, a clear idea of the relation of these folds to
the stomach, as well as to the points of origin of the lymphatic trunks which invade
it, is imperative for an understanding of the development of these vessels. As the
relations of this part of the peritoneum in the pig are slightly different from those in
the human body, a brief description of them is necessary. The dorsal mesogastrium
which later forms the great omentum, contains the spleen between its layers. The
spleen lies ventralward, close along the greater curvature of the stomach, and has
two ligaments. The first of these is the gastro-splenic, that part of the omentum
connecting the spleen with the greater curvature of the stomach. The second is
the splenic ligament, that part of the omentum which forms the posterior wall of
the omental bursa and from the hilum of the spleen is continuous with the peritoneum covering the Wolffian body, the general mesentery of the intestine and the
mesentery of the duodenum. The transverse colon, with its mesentery, lies free from
the omentum. The duodenum has a broad, fan-shaped mesentery which continues
cephalad to that part of the omentum forming the posterior wall of the omental
bursa and caudad to the common mesentery of the small intestine. The ventral
mesentery remains as the gastro-hepatic ligament, connecting in the usual manner
the lesser curvature of the stomach with the hilum of the liver.
 
 
The retroperitoneal sae, discovered by F. T. Lewis, has been well described by
Sabin, Baetjer, Heuer, and other workers in this laboratory. It is a triangular
structure which lies at the base of the mesentery at the level of the coeliac axis.
There are two small indentations along its sides, made by the adrenal bodies, which
thus divide the sac into two lobes. From the posterior lobe, which is the larger, arise the lymphatics of the intestine and of the abdominal structures, while from
the anterior lobe spring vessels to the stomach, spleen, duodenum, diaphragm, and
lungs (text-figure 2). It is this anterior portion of the sac with which we are primarily concerned in this study. The entire sac is obliterated during development,
being the primordium for the chain of lymph-glands which reach from the cceliac
axis to the bifurcation of the aorta.
 
 
The gastric vessels arise by two main trunks from the anterior lobe of the retroperitoneal sac. The right trunk is much larger than the left and passes behind the
stomach to the lesser curvature, where it invades the stomach at three different
points: (1) the opening of the esophagus, (2) the center of the lesser curvature, and
(3) the pyloric extremity of the lesser curvature. These three sets of vessels to the
stomach are well shown by a comparison of figures 6 and 7. It can be seen (fig. 6)
that another vessel of considerable size is given off from the right trunk, or arises
as a separate trunk from the anterior part of the retroperitoneal sac, and passes
through the mesentery to the duodenum (A. Duo. V.). It then extends along the
duodenum to the pylorus, where it anastomoses freely with the pyloric vessels,
reaching the stomach from its posterior surface (fig. 4) .
 
 
 
TEXT-Fig. 2. Diagram of the retroperitoneal sac showing the relation of the gastric trunks as they leave its anterior end. The early lymphatics extending to the pillars of the diaphragm are also illustrated.
 
A., Adrenal; D. P., pillar of the diaphragm; D. V., diaphragmatic vessels; H. V., hepatic vessels; K., kidney; R. G. T., right gastric trunk; R. P. S., retroperitoneal sac; V. S. M., vessels of splenic mesentery, W. B., Wolffian body.
 
 
 
The left gastric trunk, or splenic trunk, as it may be called from its distribution, divides into two branches. One passes directly to the cardiac pouch and is not shown in the figures; the other passes through the splenic ligament to the hilum of the spleen, the interior of which it has never been seen to enter, and then traverses the gastro-splenic ligament to the center of the greater curvature of the stomach where it ramifies to right and left (fig. 4). These lymphatics then anastomose, over both the anterior and the posterior walls, with those from the lesser curvature, where connections are formed with the lymphatics of the esophagus and duodenum (cf. figures 4 and 5, plate 1).
 
 
After this brief description of the general pathways along which lymphatic invasion of the stomach takes place, the characteristics of each invading set of vessels and their part in forming the general lymphatic plexuses remain to be considered.
 
 
TEXT-Fig. 3. Pig embryo, 100 mm. long. Diagrammatic transverse section of the stomach and spleen with their peritoneal ligaments. The arrows which begin from the
retroperitoneal sac show the directions in which lymphatic invasion of the stomach takes place. In this specimen the stomach
is collapsed. The hilum
of the spleen is marked by
vessels of the splenic mes-
entery (V. S. M.); also
the greater curvature of
the stomach may be
located both by its vessels
(V. G. C.) cut in cross-
section and by the attach-
ment of the gastro-splenic
ligament.
 
 
The stomach may be regarded as being invaded from the posterior side at the
lesser curvature by the right trunk, and anteriorly along the greater curvature
by the left trunk. The posterior invasion of the lesser curvature takes place
along the gastro-hepatic ligament (the primitive ventral mesentery), while the
anterior invasion at the greater curvature is by way of the splenic and gastrosplenic ligaments (the primitive dorsal mesentery of the stomach) and the mesentery
of the duodenum (text-figure 3). This arrangement offers a striking contrast to
the manner in which the lymphatics reach the intestine. Here, straight trunks
grow out from the retroperitoneal sac through the mesentery and, on reaching the
wall of the intestine, divide into right and left branches to surround the gut. In the
case of the stomach the right and left branches leave the retroperitoneal sac directly
and pass to the stomach by way of two separate folds of related peritoneum.
 
 
The earliest stage injected was an embryo 28 mm. in length (fig. 7). The
vessels arising from the retroperitoneal sac can be seen just reaching the stomach.
This is a very early stage and the injected vessels are those arising from the right
gastric trunk of the retroperitoneal sac. In this specimen the spleen and liver have
been removed. It has never been possible to inject the splenic vessels (left gastric
trunk) at this stage, but the mode of entrance of the right gastric trunk is well
illustrated. Figure 7 shows the primitive mass of lymphatics which later becomes
grouped into the right gastric trunk and distributed to the stomach in three parts :
 
 
at the esophageal opening, at the center of the lesser curvature, and at the pylorus.
It is from this mass of lymphatics that most of the gastric vessels develop. It will
be noted in the figure that the lymphatics to the esophageal opening already suggest
the ring which is later to become so characteristic. The central mass to the lesser
curvature can be seen emerging from behind the hepatic vessels which are cut off
in the drawing. These vessels to the lesser curvature are shown spreading out over
the anterior surface of the stomach ; they also extend over the corresponding area
on the posterior wall. Two or three small vessels (P. V.) pass forward to the
pylorus and it is important to note that they always reach this structure at its
posterior wall. It is these vessels which will later anastomose with both the ascend-
ing duodenal vessels (A. Duo. V.) and the vessels of the greater curvature (V. G. C.),
as shown in figure 4.
 
 
Growth is very rapid and in slightly older specimens (35 to 45 mm.), in which
the splenic vessels have also appeared, the rapid invasion from the lesser cuvature is
apparent. The vessels reaching the esophagus have by this time formed a complete
subserous, periesophageal ring. This ring continues to develop and in older specimens forms a dense, circular plexus around the esophagus, from which branches pass
in all directions to ramify over the stomach wall (fig. 8). The annular structure of
this plexus is not only manifest as a subserous set of vessels, but is maintained in
the depths of the stomach wall in this region as development proceeds.
 
 
The vessels which reach the stomach at the center of the lesser curvature are
by far the most numerous of any of the groups. As they traverse the gastrohepatic ligament they are in direct communication with the lymphatics of the liver,
which pass through this structure and also take origin from the retroperitoneal sac
(fig. 2) . On reaching the stomach they branch over both the anterior and posterior
walls and form numerous anastomoses with the vessels from the esophageal ring,
as well as with the lymphatics reaching the lesser curvature at the pylorus. These
pyloric vessels form the smallest group of lymphatics invading the stomach. They
spring from the right trunk just lateral to the large group at the center of the lesser
curvature and pass through the gastro-hepatic ligament to the posterior surface of
the pylorus, over which they anastomose freely with the set of vessels reaching the
pylorus by way of the mesentery of the duodenum.
 
 
This latter set of lymphatics (fig. 4), to which we may refer as the ascending
duodenal vessels, forms a trunk of considerable size. They can be injected only in
the younger embryos, due to the fact that one or more lymph glands are later
formed in the mesentery of the duodenum at the pyloro-duodenal junction. Their
rich anastomosis with the other gastric vessels presents a subject of unusual interest,
inasmuch as it is not generally stated that lymphatic drainage of the stomach takes
place partly by way of the mesentery of the duodenum. The magnitude of early
vessels invading the stomach from this source and the extent of their anastomoses
with the gastric vessels proper give proof of a well-defined pathway by which
lymphatic drainage from the stomach may take place. Figures 4 and 6 show the
extent of the anastomosis of these ascending duodenal vessels with the other vessels
of the pylorus.
 
 
The origin of the ascending duodenal group is somewhat varied in the different
specimens. In some, these vessels spring from the right gastric trunk as it leaves
the retroperitoneal sac; in others, they arise from the sac itself just posterior to the
right gastric trunk. In their course through the duodenal mesentery they present
no unusual features, but the lymph-glands, later formed along their course at the
pyloro-duodenal junction, offer a striking point of difference from the glands of the
other vessels leaving the stomach. These glands prevent the injection of the
duodenal lymphatics from points on the stomach and this fact most likely accounts
for the failure to recognize such a connection between gastric and duodenal lmphatics by methods such as have been hitherto employed to demonstrate them.
 
 
The left gastric trunk, arising from the retroperitoneal sac, immediately
divides into two branches. The lesser branch passes by way of the extreme left
portion of the omental bursa to the anterior surface of the stomach at the base of
the cardiac pouch. The cardiac pouch is a transient, embryonic structure. In the
pig, during embryonic life, there is a slight annular constriction of the stomach wall
near the cardiac end, which gives to that portion of the stomach a pouch-like
appearance (fig. 5). This structure becomes less evident as development proceeds
and in very late stages is scarcely perceptible. The lesser branch of the left cardiac
trunk is the principal source of invasion of the pouch and forms rich anastomoses
with the vessels reaching the stomach at the center of the lesser curvature and
esophageal opening. The greater branch of the left gastric trunk enters the omental
bursa just medial to the lesser branch. It passes by way of the posterior wall of the
omental bursa (which in this region constitutes the splenic ligament) to the hilum of
the spleen; from this point these vessels pass by way of the gastro-splenic ligament
to the center of the greater curvature of the stomach (figs. 4 and 5). The number
of vessels comprising this set varies from two to four. It is always difficult to be
certain of the exact number, as they are situated very close together in a densely
entwined mass. They have never been observed to enter the spleen, and sections
taken through the point where they pass the hilum of that organ have consistently
failed to demonstrate a trace of injection mass within its interior. So it may be
said that these vessels appear in no way related to the spleen itself but merely take
advantage of its folds of peritoneum to make their way to the stomach. They
reach that organ on the greater curvature, at a point about midway between the
cardia and pylorus, and from this point their growth proceeds in opposite directions.
Approximately half of them pass to the right, along the greater curvature, to meet
the pyloric vessels from the duodenum which grow along this course ; the other half
pass along the greater curvature, to the left, where they meet anastomosing vessels
from the cardia, esophageal ring, and lesser curvature (fig. 4). All along their
course on the greater curvature these vessels give off branches at right angles to
themselves, which extend over the anterior and posterior walls of the stomach to
meet similar branches given off from the great mass of lymphatics of the lesser
curvature.
 
 
Concomitant with the growth of the subserous trunks, growth of the other
plexuses takes place. Sprouting branches from the early trunks of the subserosa
dip down into the stomach wall and, as the muscular layers are traversed, the plexus
between the muscular layers is formed . This plexus extends throughout the stomach
wall, but its vessels are of smaller caliber and its meshes much less dense than those
of the other plexuses. It should be borne in mind, however, that vessels lying in
dense, muscular tissue fill less readily with injection mass than those situated in the
loose tissues of the submucosa and subserosa; therefore, the appearance of the
muscular plexus may be less dense than it really is. This point considered, the small
size of the vessels composing the plexus of the muscularis and their striking constancy
of arrangement in all well injected specimens nevertheless are facts which tend to
show that this plexus is a relatively scanty one.
 
 
On reaching the submucosa these vessels form the most extensive plexus of
the stomach wall, the main plexus of the submucosa. Here lymphatic growth
takes place very rapidly. At an early stage (20 to 40 mm.) an extremely dense
plexus, several layers in thickness, composed of large, tortuous vessels, has been
formed. In embryos 70 to 100 mm. in length the entire submucosa is found to be
filled by this plexus. Its presence can be easily demonstrated throughout the
entire stomach by injecting directly into the submucosa. As it nears the pylorus
its vessels become smaller and many of them appear to end blindly in this region ;
however, a few of them have been seen to anastomose with those of the deep plexus
of the duodenum. In view of the general tendency toward anastomosis exhibited
by the lymphatics of contiguous tissue, which is especially marked in the lymphatics
of the subserous plexuses of the stomach and duodenum, this scanty connection
between the submucosal plexuses of these two organs can scarcely be considered as
representing the true morphology of the lymphatics in this region. It is evident
that the layers of the stomach wall at the pylorus are compressed by the tone of the
pyloric musculature, as are also the lymphatic channels of the submucosa. Such a
barrier proves quite effective in preventing complete injection of the vessels of this
region. The character of the apparent endings of the vessels of the submucosa at
the pylorus favors such a view. Instead of forming a complete plexus at this
point, most of the vessels end blindly and at different points along the pylorus, thus
giving the exact picture of an incomplete lymphatic injection elsewhere in the body.
From the injections we are justified in saying only that the pathway between the
submucous plexuses of the stomach and duodenum is not easily traversable during
tonic contraction of the pylorus. A sufficient number of anastomoses between
these two plexuses has been demonstrated to show that they are connected and, by
analogy to the lymphatics of the rest of the gastro-intestinal tract, one would expect
ready communication between them during relaxation of the pyloric sphincter.
 
 
The further growth of the lymphatics in the wall of the stomach takes place from this dense submucosal plexus. Many smaller vessels grow still farther inward and form the scanty plexus adjacent to the muscularis mucosse. This plexus lies at the base of the gastric glands and sends branches between them.
 
 
Figure 8, plate 3, is from a complete injection of the stomach of a pig measuring
150 mm. It has been cut along the greater curvature and spread out to show
especially well the marked esophageal ring of lymphatics. This ring constitutes one of the most striking characteristics of all injections of the stomach made before
the appearance of glands in this region. Its formation by vessels arising from the
retroperitoneal sac is well shown; branches may be observed passing in every
direction from all points of it ; those going to the cardiac pouch are well seen over
the anterior wall, while in the depths on the posterior wall are seen the vessels of
the left gastric trunk with which they anastomose. Those vessels passing to the
anterior wall are shown as a series of parallel trunks in the serosa which lead into
the deeper, much more extensive plexus of the submucosa within the depths of the
stomach wall. These serosal trunks, as well as the plexus of the submucosa, anastomose with the corresponding trunks and plexus arising from the vessels of the greater
curvature ; they remind one of similar parallel trunks shown by Heuer in the development of the lymphatics of the intestine. The posterior surface of the stomach is
seen on the left side of the figure. Here the posterior position of the pyloric vessels
arising from the lesser curvature is well shown, as is also the characteristic arrange-
ment of the serosal trunks and plexuses of the submucosa.
 
 
The development of lymphatics of the diaphragm is likewise well illustrated by
these injections. Large lymphatic trunks, accompanied by the lymphatics of the
lower lobes of the lungs which arise from this source, can be seen passing from the
anterior part of the retroperitoneal sac to the pillars of the diaphragm. The
pulmonary vessels penetrate the diaphragm, while the others spread out over its
surface. Also from the gastric plexus, at the lesser curvature of the stomach, many
large vessels pass directly to the diaphragm along the ligaments of the liver and
anastomose freely with those from the retroperitoneal sac, arriving by way of the
pillars (fig. 6) . Such an invasion of the diaphragm is readily explained by the double
origin of this structure, the pillars arising from the pleuro-peritoneal membrane,
while the body of the diaphragm arises from the ventral mesentery, septum transversum, and body-wall. The embryonic lymphatics of the diaphragm are enormous
and soon cover the entire structure with a dense plexus. The active function of the
diaphragm as an agent of absorption is at once apparent by a glance at its rich
supply of lymphatics.
 
 
Here a word may be said about the lymphatics of the esophagus and their
relation to those of the stomach. Its vessels are derived from two sources. Those
of the lower end arise from the gastric vessels forming the periesophageal ring
at the cardia of the stomach, from which they spring as direct outgrowths and extend upward to a point on the esophagus about midway between the bifurcation
of the bronchi and the cardia of the stomach. Here they meet lymphatics which
have extended to the esophagus from the bronchial plexuses at the hilum of the
lungs, primarily arising from the thoracic duct. The lymphatic plexuses of the
esophagus are completed by the anastomosis of the vessels from these two sources.
In their general arrangement they are similar to those of the stomach wall, with
which they are continuous. Lymphatic drainage from the esophagus takes place
in two directions, the lower portion following the general path for gastric drainage
described for the cardia of the stomach, while the upper portion drains to the
bronchial plexuses.
 
 
Information thus obtained from the injection of embryos did not necessarily
justify conclusions in regard to the lymphatic drainage in the fully developed and
adult stomach. Injections were therefore made of the stomachs of kittens, cats,
and adult pigs. In all specimens thus prepared lymphatic drainage was found
to be similar to that deduced from the study of the injected embryos. This
was clearly illustrated in the fresh stomach of a kitten 24 days old. Three
large glands were seen at the lesser curvature in the gastro-hepatic ligament, one
at the base of the splenic ligament, and one lying in the pyloro-duodenal flexure.
By injecting directly into the submucosa the paths of drainage were readily seen by
the spread of the injection mass through the lympathic plexuses of the stomach wall
and its appearance in the adjacent nodes. Injections were made at several sites:
(1) By injecting directly into the plexus of the submucosa, in the central region of
the anterior and posterior surfaces, the injection mass quickly appears in the nodes
of the lesser curvature; also, some of the vessels along the greater curvature are
filled by part of the injection flowing in that direction. Thus, the flow from the
anterior and posterior walls of the stomach was seen to pass in two principal
directions, toward the lesser and toward the greater curvatures, the major part
going to the former. (2) Injections near the pylorus and from some distance
along the adjacent greater curvature quickly flowed to the gland at the pyloro-duodenal flexure, while, at the same time, an appreciable extent of the anterior and
posterior walls and the greater curvature was also filled. (3) When the plexus of
the submucosa near the attachment of the gastro-splenic ligament was filled, the
vessels passing from the greater curvature toward the spleen, as well as those from
the spleen to the large gland at the base of the splenic ligament, were injected.
Likewise, from this point of injection, flow occurred freely in all other directions, part
going toward the lesser curvature and part toward the pylorus.
 
 
Jamieson and Dobson made a careful study of the lymphatic drainage in the
fully developed human stomach by means of the method of injection and found the
main groups of glands to be associated with the larger arteries of the stomach and
spleen. Along the course of the coronary artery they found a group of glands
forming a periesophageal ring with another group in the gastro-hepatic ligament.
Associated with the splenic artery, in the gastro-splenic ligament, was another group
of glands. Along the course of the hepatic artery and in the bend of the duodenum,
along the gastro-duodenal artery, still other groups were observed. By injecting
directly into the submucous plexus of the stomach wall at various points, the course
of the flow of lymph to these glands was studied. From the results so obtained these
observers were led to believe that any points of division between areas drained by
any definite gland or group of glands were quite arbitrary. They found the plexus
of the muscularis to be a very scanty one. The lymphatics of all plexuses of the
stomach- wall near the cardia were seen to be continuous with those of the esophagus,
whose wall contains lymphatics arranged similarly to those of the stomach. Definite
communications were also found between both subserous and submucous plexuses
of the pyloric portion of the stomach and the duodenum. These connections of the subserous plexuses were found to be rather scanty and mostly on the posterior walls
of these organs, while the submucous anastomoses were quite numerous.
 
 
Such observations are in strict accordance with the ideas one would be led to
form from a study of the development of the gastric lymphatics. The three points
of invasion from the lesser curvature correspond to the chains of glands along the
ascending and descending branches of the coronary artery and the hepatic artery.
The lymphatics reaching the stomach by way of the splenic ligaments, however,
appear to indicate that lymphatic invasion does not always take place along blood-vessels, since the lymphatics traversing these ligaments are not accompanied by any
blood-vessels of appreciable size. More likely, it seems that related folds of peritoneum determine the pathways by which the lymphatics reach the stomach; in many
cases the arteries take the same course. The greater number of anastomoses
between the vessels of the pylorus and duodenum than has commonly been observed,
and the fact that most of the connections between the subserous plexuses of these
organs are located on their posterior walls, are points which can be readily understood from the development of the ascending duodenal group of vessels, which
are much more numerous in this region (figs. 4 and 6).
 
 
So, from the combined evidence offered by injections of developing lymphatics
in several embryonic stages, and the further injection of these vessels after the
lymphatic plexuses of the stomach have been completely formed, the lymphatic
supply of this organ is seen to be one of the richest in the entire body. Due to the
homogeneity of its plexuses, no strict division of its areas of drainage can be made
that will remain constant in any number of cases. So readily is any portion of the
stomach injected from any other part that, in all probability, the lymphatics of
the entire organ could be filled by a single injection into the submucosal plexus, if
performed slowly enough and with proper pressure. The greatest part of the
gastric drainage certainly takes place by way of the lesser curvature, but the other
two routes by way of the splenic ligaments and duodenal vessels are of quite appreciable capacity. Many factors, such as peristalsis, muscle tone, venous engorgement, pressure in the lymphatic vessels themselves, and (in pathological stomachs)
various degrees of obstruction must determine the relative amount of drainage by
these three outlets, the sources of whose output are in continuity and show no zonal
lines of demarcation.
 
 
==Conclusions==
 
# From a study of development of the lymphatics in the stomach of the embryo pig, it is found that they invade that organ at two principal points, viz., the lesser curvature, by way of the gastro-hepatic ligament, and the greater curvature, via the ligaments of the spleen.
# Arising in common with the gastric lymphatics is a large trunk which passes to the duodenum, then up along the duodenum to the pylorus, anastomosing freely with the lymphatics on the posterior surface of the stomach.
# Part of the lymphatics invading the stomach at the lesser curvature, early in their growth, form a dense periesophageal plexus of vessels in the subserosa.
# From this periesophageal ring, as well as from the other vessels reaching the stomach at both lesser and greater curvatures, branches are given off at right angles on both the anterior and posterior walls of the stomach. These vessels finally meet and encircle the stomach in a segmental manner similar to that' described by Heuer for the intestine. There are a number of connections between these segmental subserous trunks, forming them into a subserous plexus.
# During the development of this plexus numerous branches from its trunks pierce the layers of the stomach and form other gastric plexuses. All of these are homogeneous layers of lymphatic vessels.
# The richness of the gastric plexuses and their numerous anastomoses preclude the theory of any sharply defined areas whose drainage would take place in constant given directions.
# There are four general pathways by which lymphatic drainage may take place: (a) the lesser curvature, (b) the greater curvature, (c) the duodenum, and (d) the esophagus.
 
 
I wish to thank Professor F. R. Sabin and Dr. R. S. Cunningham for the valuaable assistance they have given me in this work, and to express my appreciation to
Mr. J. F. Didusch for the illustrations.
 
 
==References==
 
BAETJER, W. A., 1908. The origin of the mesenteric sac and thoracic duct in the embryo pig. Amer. Jour. Anat., vol. 8.
 
CASH, J. R., 1917. On the development of the lymphatics in the heart of the embryo pig. Anat. Rec., vol. 13.
 
:, 1919. On the development of the lymphatics of the stomach of the embryo pig. Anat. Rec., vol. 16, p. 145.
 
CUNEO, B., 1902. Systemelymphatique,(PoirierandCuneo). Traite d'anatomie humaine, Poirier and Charpy.
 
CUNNINGHAM, R. S., 1916. [[Book_-_Contributions_to_Embryology_Carnegie_Institution_No.12|On the development of the lymphatics of the lungs in the embryo pig.]] Contributions to Embryology, vol. 4, Carnegie Inst. Wash. Pub. No. 224.
 
 
GRAY, H. Anatomy. Lewis ed.
 
HEUER, G., 1909. The development of the lymphatics in the small intestine of the pig. Amer. Jour. Anat., vol. 9.
 
JAMIESON, J. R., and J. F. DOBSON, 1907. The lymphatic system of the cjecum and appendix. Lancet.
 
KEIBEI, & MALL, 1912. Human Embryology.
 
MALL, F. P., 1896. The vessels and walls of the dog's stomach. Johns Hopkins Hosp. Reports, vol. 1.
 
SABIN, F. R., 1913. The origin and development of the lymphatic system. Johns Hopkins Hosp. Reports. vol. 17.
 
==Descriptions of Plates==
 
 
===Plate 1===
 
Fig. 4. Pig embryo, 60 mm. Anterior view of stomach showing relation of the lymphatics of the lesser curvature to
those of the liver and diaphragm. The vessels of the splenic mesentery may be seen extending from
beneath the spleen to the greater curvature along which they have grown. Anastomosis has already
taken place between these vessels, growing toward the right along the greater curvature, and lym-
phatics from the lesser curvature, which may be seen coming from the posterior wall of the pylorus.
Anastomosis of the ascending duodenal vessels at this point is also shown. (X19.)
A. Duo. V., Ascending duodenal vessels; D., diaphragm; D. V., diaphragmatic vessels; H., liver; H. V.
hepatic vessels; S., spleen; V. G. C., vessels of the greater curvature; V. L. C., vessels of the lesser curva-
ture; V. S. M., vessels of the splenic mesentery.
 
Fig. 5. Pig embryo, 40 mm. Posterior view of injected stomach showing the main mass of lymphatics which reach
the stomach at the lesser curvature and their growth over the posterior stomach wall. The vessels
of the splenic mesentery are also here seen to anastomose with those extending from the lesser curvature.
These vessels, which reach the stomach by way of the gastrosplenic ligament, are also shown beginning
to extend to the right and left along the greater curvature. The spleen lies in its usual position. The
cardiac pouch is well marked in this specimen. (X 20.)
 
C. P., cardiac pouch; 0., esophagus; P., pylorus; S., spleen; V. G. C., vessels of the greater curvature;
V. L. C., vessels of the lesser curvature; V. S. M., vessels of the splenic mesentery.
 
===Plate 2===
 
Fig. 6. Pig embryo, 50 mm. View of stomach from right. The organ has been tilted forward to show the great mass
of lymphatics arising from the retropcritoneal sac behind it. The vessels to the duodenum and their
extension toward the stomach are shown. Lymphatics from the retroperitoneal sac, some of which
ramify over the diaphragm, others piercing it to reach the lungs, are also seen. The thoracic duct lies
at the left of the illustration. (X15.)
 
A. Duo. V., ascending duodenal vessels; D., diaphragm; Duo. M., mesentery of the duodenum; D. V.,
lymphatics of the diaphragm; H., liver; H. V., hepatic vessels; L., lung; Pul.. V., pulmonary
vessels, R. P. S., anterior end of retroperitoneal sac; T. D., thoracic duct; V. L. C., vessels of the lesser
curvature.
 
Fig. 7. Embryo pig, 30 mm. long. Anterior view of specimen from which the liver has been removed but the gastro-
hepatic ligament left intact. The dark line, along whose edges are seen cut ends of lymphatics, marks
the area from which the liver has been taken. These open vessels are those of the hepatic capsule. The
manner in which the lymphatics of the lesser curvature reach the stomach by way of the gastro-hepatic
ligament and their relations to the lymphatics of the liver are shown here. The branch of the left
gastric trunk passing to the cardiac pouch is also illustrated. The diaphragm may be seen posterior to
the cut edge of hepatic peritoneum. (X17.5.)
 
C. P., cardiac pouch; D., diaphragm; Duo., duodenum; D. V., diaphragmatic vessels; H. V., hepatic
vessels; L. G. T., left gastric trunk; 0., esophagus; P. V., pyloric vessels; V. L. C., vessels of the lesser
curvature.
 
===Plate 3===
 
Fig. 8. Embryo pig, 150 mm. long. Dorsal view of stomach which has been cut along its anterior surface parallel
to the greater curvature and the specimen spread out to show the relation of the lymphatics of the
lesser curvature to those of the anterior and posterior walls of the stomach. The greater curvature is
marked by the vessels which have their course along its border (V. G. C.). It may be noticed that
the superficial plexus is composed of vessels whose general course is at right angles to the curvatures,
while the deep plexus consists in a much denser, homogeneous mass of lymphatics. (X12.)
A. W., anterior wall of stomach; D. G. P., deep gastric plexus (plexus of the submucosa) ; 0., esophageal
opening; P., pylorus; Pan., pancreas; P. W., posterior wall of stomach; R.P.S., retroperitoneal sac;
S., spleen; V. G. C., vessels of the greater curvature; V. L. C., vessels of the lesser curvature.
 
 
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