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iliac glands, (2) efferents from the sub-aortic glands, (3) efferents from the sacral glands, (4) some efferents from the hypogastric glands, (5) efferents from the main inferior mesenteric glands, (6) the lymph vessels from the testes and epididymides and their coverings in the male, and from the ovaries, the uterine tubes, and the upper part of the uterus in the female, (7) lymph vessels from the
FIG. 817.-SEMI-DIAGRAMMATIC VIEW OF THE LYMPH GLANDS AND VESSELS OF THE PROXIMAL PARTS OF THE LOWER EXTREMITIES, THE PELVIS MAJOR AND THE POSTERIOR PART OF THE ABDOMEN.
kidneys, (8) lymph vessels from the suprarenal glands, (9) lymph vessels from the muscles of the back and of the posterior wall of the abdomen.
The efferents of the lumbar glands form two common lumbar lymph trunks, which pass to the cisterna chyli.
THE LYMPH VESSELS OF THE ABDOMINAL VISCERA AND THE
The Lymph Vessels of the Abdominal Part of the Alimentary Canal. -The lymph vessels in the walls of the alimentary canal form four plexuses: (1) a mucous plexus, in the mucous membrane, (2) a submucous plexus, in the submucous tissue, (3) a muscular plexus, between the two muscle coats, (4) a subserous plexus which lies in the areolar tissue between the peritoneal covering and the outer muscular coat. The four plexuses communicate freely with each other. The lymph is eventually collected from the subserous plexus and carried to the various groups of lymph glands. The vessels which carry away the lymph from the sub
serous plexuses of the various parts of the alimentary canal are spoken of in the following account as the lymph vessels of those parts.
The Lymph Vessels of the Stomach.-The lymph vessels of the stomach communicate freely with the lymph vessels of the oesophagus on the one hand and those of the duodenum on the other.
From the point of view of lymph outflow the area of each surface of the stomach may be divided into four parts. First a small right portion of the region of the pyloric canal, and, second, the remaining larger portion which is subdivided into three parts by two lines: (1) A line from the apex of the fundus to the pyloric canal along the junction of the upper and right two thirds with the left and lower third, (2) a line, parallel with the oesophagus, dividing the left and lower part into left and right portions (J. and D.). It must be understood, however, that the lymph vessels of the various areas communicate freely with one another (Fig. 815).
The Lymph Vessels of the Region of the Pyloric Canal pass (a) partly to the anterior left gastric glands, (b) partly to the right supra-pancreatic lymph glands, and (c) partly to the lower biliary group of lymph glands. If the right gastric gland is present some of the vessels of the upper pyloric region go to it, and in some cases vessels from the pyloric region pass directly to the posterior left gastric lymph glands.
The Lymph Vessels from the Right Upper Area of the larger portion of the stomach pass (a) to the anterior left gastric lymph glands, (b) to the posterior left gastric lymph glands, (c) to the paracardial lymph glands.
The Lymph Vessels from the Left Section of the Left and Lower Portion of the stomach pass along the gastro-splenic ligament to the splenic glands, which are occasionally present near the hilum of the spleen, and partly to the left supra-pancreatic lymph glands.
The Lymph Vessels from the Right Part of the Lower and Left Area follow the course of the right gastro-epiploic artery and terminate in the sub-pyloric glands.
The Lymph Vessels of the Duodenum are apparently few and difficult to inject; they communicate with those of the stomach above and the jejunum below, and the collecting vessels which pass from the subserous plexus end in the biliary, the sub-pyloric, and the mesenteric lymph glands.
The Lymph Vessels of the Jejunum and Ileum, with the exception of those from the terminal part of the ileum, pass to the mesenteric lymph glands. The lymph vessels from the terminal part of the ileum go to the ileo-colic lymph glands.
The Lymph Vessels of the Cæcum, the Vermiform Process, and the Ascending Colon pass to the ileo-colic lymph glands, either directly or after having traversed glands which lie nearer to the walls of the various parts of the gut.
The Lymph Vessels of the Right Colic Flexure and the Transverse Colon pass to the meso-colic and the superior mesenteric lymph glands.
The Lymph Vessels of the Left Colic Flexure, the Descending Colon, the Iliac Colon, and the Pelvic Colon pass to the inferior mesenteric lymph glands. From those glands the greater part of the lymph is conveyed to the lumbar lymph glands, but part passes to the mesenteric lymph glands and part to the common intestinal lymph trunk.
The Lymph Vessels of the Liver.-The lymph vessels of the liver are described as forming superficial and deep groups. The superficial vessels pass to subserous plexuses from which collecting vessels arise.
The collecting vessels from the superior, anterior, and right lateral surfaces converge to a series of posterior and anterior efferent trunks.
The posterior collecting trunks form three groups: (1) a right group, which runs through the right triangular ligament of the liver and then downwards and medially on the posterior wall of the abdomen, to the middle supra-pancreatic lymph glands; (2) the middle group runs towards the inferior vena cava, passes with it through the diaphragm, and ends in the posterior mediastinal lymph glands; (3) the left group passes through the left triangular ligament to the posterior left gastric glands and the posterior paracardial glands.
The anterior collecting trunks are inferior and superior. The inferior pass from the anterior part of the right lobe, turn round the lower border, and end in the hepatic lymph glands. The superior group pass to the falciform ligament. Some turn posteriorly towards the inferior vena cava, pass through the diaphragm with it and end in the posterior mediastinal lymph glands; others turn forwards and downwards to the round ligament, which they accompany to the porta hepatis where they join the hepatic glands. The remaining vessels pass upwards to the anterior part of the diaphragm which they perforate, and they end in the anterior mediastinal glands.
The superficial collecting vessels of the inferior surface of the right lobe pass (a) backwards to the inferior vena cava and along that vessel to the posterior mediastinal glands, (b) to the cystic gland of the biliary chain. The collecting vessels of the lower part of the left lobe end in the hepatic glands. The collecting vessels of the caudate lobe pass partly to the posterior mediastinal glands, along the inferior vena cava ; and partly to the hepatic lymph glands in the porta hepatis.
The Deep Lymph Vessels of the Liver pass to ascending and descending collecting trunks. The ascending trunks follow the hepatic veins and the inferior vena cava and end in the posterior mediastinal lymph glands. The descending collectors accompany the bile-ducts, the branches of the portal vein, and the branches of the hepatic artery, and terminate in the hepatic lymph glands.
The Lymph Vessels of the Gall Bladder. The lymph vessels from the gall bladder terminate chiefly in the cystic gland but some pass to other members of the biliary chain.
The Lymph Vessels of the Pancreas.-The efferent vessels from the pancreas end in the adjacent glands, that is, some pass to the sub-pyloric, some to the supra-pancreatic, some to th mesenteric glands, and some to the posterior left gastric lymph glands.
The Lymph Vessels of the Spleen. The collecting vessels from the spleen pass to the splenic lymph glands which occasionally lie near the hilum of the spleen and the left supr.pancreatic lymph glands.
The Lymph Vessels of the Kidneys.-The lymph vessels of each kidney run along the renal blood-vessels and terminate in the lumbar glands, especially in the pre- and para-aorti lymph glands.
The Lymph Vessels of the Ureters. The lymph vessels from the abdominal part of each ureter pass to the lumbar and the common iliac and the sub-aortic lymph glands.
The Lymph Vessels of the Suprarenal Glands anastomose with the vessels of the kidneys and pass to the lumbar and to the posterior mediastinal lymph glands.
The Lymph Vessels of the Diaphragm.-The collecting lymph vessels from the diaphragm pass to the thoracic lymph glands, that is, to the anterior and posterior mediastinal lymph glands, and lower sternal glands.
The Lymph Vessels of the Posterior Wall of the Abdomen terminate in the lumbar lymph glands.
DEVELOPMENT OF THE BLOOD-VASCULAR SYSTEM.
THE ARTERIES AND THE HEART.
In the general account of the development of the primitive vascular system and the establishment of the foetal circulation, given in a previous chapter, it was pointed out that the germ of the whole blood-vascular system appears in the wall of the yolk-sac as a series of strands of cells which constitute the
angioblast. Some of the angioblast cells remain in situ and form the blood-vessels of the walls of the yolk-sac and the corpuscular contents of the blood-vessels; other angioblastic cells wander into the embryonic area and form the bloodvessels of the embryo; whilst still others become located in the developing liver and other organs, where they become foci for the formation of new blood corpuscles.1
The first blood
Dorsal intersegmental branches
Common trunk formed
Vena umbilicalis impar Umbilical arteries
vessels developed in the FIG. 818.-SCHEMA OF CIRCULATION OF AN EMBRYO, 135 MM. LONG, WITH embryonic area are the SIX SOMITES. (After Felix, modified.)
primitive aorta. They
appear, either just before the embryonic area begins to be folded into the form of the embryo or as the folding is commencing, in the pericardial or anterior region of the embryonic area, where they are continuous with the earlier-formed vessels on the wall of the yolk-sac. From the pericardial region they extend caudalwards, one on each side of the notochord, and as they
FIG. 819.-SCHEMA OF VASCULAR SYSTEM OF AN EMBRYO, 2.6 MM. LONG,
pass caudalwards they give off a series of dorsal and ventral branches. The dorsal branches are intersegmental in arrangement, inasmuch as they lie in the intervals between the mesodermal somites. The ventral branches are more irregular, and are neither strictly segmental nor intersegmental in arrangement; moreover, they are not only distributed to the wall of the alimentary canal, but they also pass across it to the yolk-sac. Further, those which are situated nearest the tail anastomose together, on the side wall of the hind-gut area, forming
a plexus, and it is from that plexus, on each side, that the umbilical artery is prolonged along the body-stalk to the chorion (Figs. 818, 819).
As the head fold forms, the cephalic part of each primitive aorta is bent into the form of a loop, and the whole vessel assumes a hook-shaped form. The long or dorsal limb of the hook,
which lies along the dorsal wall of the primitive alimentary canal, is the primitive dorsal aorta; the bend of the hook is the first aortic arch; the short ventral limb of the hook, which lies in the ventral wall of the fore-gut and the dorsal wall of the pericardium, is the primitive ventral aorta; it is continuous, at the anterior margin of the umbilical orifice, that is at its own caudal end, with the vitelline vein, which is carrying blood from the yolk-sac to the embryo. The condition described is that found in embryos about 14 mm. long, possessing six mesodermal somites (Fig. 818).
In embryos in which the mesodermal somites have increased to fourteen pairs the posterior, or caudal, portions of the primitive ventral aortæ have fused together to form a single heart (Fig. 819).
The Primitive Heart. The primitive heart lies in the dorsal wall of the pericardium and, therefore, in the ventral wall of the fore-gut. As it grows more rapidly in length than the wall to which it is attached, it bends upon its long axis and bulges ventrally into the interior of the pericardium. As it projects into the pericardium it pushes before it the immediate bounding wall of the pericardial cavity, which thus becomes converted into the visceral pericardium. The visceral pericardium surrounds the heart, and passes from its dorsal border to the ventral wall of the fore-gut as a double layer which constitutes the dorsal mesocardium.
The portion of each primitive ventral aorta which lies cephalwards of the heart forms the ventral root of the first aortic arch. At this stage the primitive dorsal aortæ are still separate from one another, and each gives off a series of dorsal intersegmental branches, and a series of ventral branches which pass across the side walls of the primitive gut on their way to the wall of the yolk-sac.
The caudally situated ventral vessels, as in the earlier stage, form a plexus on the side walls
FIG. 820.-SCHEMA OF VASCULAR SYSTEM OF AN EMBRYO WITH TWENTY
THREE SOMITES. (Arteries after Felix, modified.)
of the primitive gut from which the umbilical arteries arise (Fig. 819).
When the embryo has attained a length of 25 mm, and possesses about twentythree mesodermal somites, the two primitive dorsal aortæ have fused together, from the tenth to the sixteenth somite, forming in the region of fusion a single dorsal aorta, which becomes the descending aorta of the adult.
At a slightly later stage the fusion of the two primitive dorsal aortæ extends caudalwards to the level of the twenty-third somite, where one of the ventral branches of each primitive
vessel becomes enlarged and forms the origin of the stem of the primitive umbilical artery. Still later the comparatively small continuations of the primitive dorsal aorta, which are continued caudalwards from the twenty-third somite to the end of the caudal region, fuse together to form the middle sacral artery-the dorsal aorta, as such, terminating at the twenty-third body somite. The Primitive Veins.-In embryos 14 mm. long two primitive veins are present on each side in the body of the embryo-the lateral umbilical veins and the vitelline veins. The lateral umbilical veins are the divisions of the vena umbilicalis impar, which returns blood from the placenta to the embryo; and the vitelline veins return blood from the yolk-sac (Fig. 819). During the time in which the embryo increases from 1.4 mm. to 2.6 mm. additional veins appear. the body and head of the embryo become larger definite venous channels are formed to return blood from them to the heart, and in association with the more rapid development of the cephalic portion of the embryo the first entirely intra-embryonic veins to appear are the anterior cardinal veins, one on each side, which return blood from the head, and from the cephalic or anterior portion of the body of the embryo. These veins are present in embryos possessing fourteen mesodermal somites, and each terminates in the common trunks formed by the union of the vitelline and umbilical veins of the same side (Fig. 819).
A little later the posterior cardinal veins, one on each side, develop in the caudal or posterior part of the body. They join the anterior cardinal veins at the level of the caudal end of the heart, and the common trunk formed by the union is the duct of Cuvier, which opens directly into the caudal part of the heart. In the meantime the venous trunk, produced by the union of the lateral umbilical with the vitelline vein, and into which the anterior cardinal vein opened, is absorbed into the heart; therefore, when the ducts of Cuvier are formed, six vessels, three on each side, open into the caudal portion of the heart-the vitelline veins, the lateral umbilical veins, and the ducts of Cuvier. Whilst these changes in the veins are taking place, two additional aortic arches are formed, one on each side. They spring from the cephalic extremity of the heart, immediately caudal and somewhat dorsal to the ventral roots of the first arch; and they terminate, dorsally, in the dorsal aorta (Fig. 820).