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between the layers of the lesser omentum, and along the lesser curvature of the stomach with the left gastric artery, to the esophagus, where it receives æsophageal tributaries. It then turns posteriorly, in the left gastro-pancreatic fold, and reaches the posterior wall of the abdomen, where it again changes its direction to run from left to right, behind the omental bursa, to the right gastro-pancreatic fold, at the root of which it opens into the portal vein.

The right gastric vein is a small vessel which is formed by the union of tributaries from the upper parts of both surfaces of the stomach. It runs from left to right along the right portion of the lesser curvature, between the layers of the lesser omentum, and terminates in the portal vein, after that vessel has entered the lesser omentum.

Vena Cystica.—The cystic vein is formed by the union of tributaries which accompany the branches of the cystic artery on the anterior and posterior surfaces of the gall-bladder; it ascends along the cystic duct and, as a rule, terminates in the right branch of the portal vein. Some small veins pass directly from the gall-bladder into the substance of the liver.

THE MESENTERIC AND SPLENIC VEINS.

Vena Mesenterica Superior.—The superior mesenteric vein commences in the right iliac fossa, in connexion with the lower part of the ileum. It ascends, along the right side of the superior mesenteric artery, in the root of the mesentery, forming a curve with the convexity to the left.

As it ascends it passes anterior to the right ureter, the lower part of the inferior vena cava, the third part of the duodenum, and the uncinate process of the head of the pancreas; and, after passing behind the root of the transverse mesocolon, it terminates, behind the neck of the pancreas, by uniting with the splenic vein to form the portal vein.

Its tributaries correspond with the branches of the superior mesenteric artery. It is formed by the union of the ileo-cæcal and appendicular veins. Anteriorly and towards the left side it receives intestinal tributaries (venæ intestinales) from between the layers of the mesentery ; the right colic and ileo-colic veins enter its right side ; the middle colic vein joins it anterior to the lower border of the head of the pancreas, and close to its termination it receives the right gastro-epiploic and the pancreatico-duodenal veins.

The right gastro-epiploic vein runs from left to right along the lower border of the stomach, between the two anterior layers of the greater omentum. It receives tributaries from both surfaces of the stomach, and near the pylorus turns posteriorly, in the right gastro-pancreatic fold of peritoneum, passes in front of the neck of the pancreas, and ends in the superior mesenteric vein.

The pancreatico-duodenal vein receives tributaries from the head of the pancreas and the adjacent parts of the duodenum; it ascends along the superior pancreatico-duodenal artery, and terminates in the upper part of the superior mesenteric vein or in the portal vein.

Vena Lienalis.—The splenic vein is formed by the union of five or six tributaries which issue from the hilum on the gastric surface of the spleen. It passes posteriorly and medially, in the lieno-renal ligament, to the kidney, then, turning to the right, it runs behind the upper border of the pancreas and below the splenic artery ; it crosses the front of the abdominal aorta, immediately below the origin of the cæliac artery, and terminates, behind the neck of the pancreas, by joining the superior mesenteric vein to form the portal vein.

Tributaries. It receives the vasa brevia or short gastric veins, the left gastro-epiploic vein, the pancreatic veins, and the inferior mesenteric vein. Occasionally the coronary vein terminates in it.

The short gastric veins are a series of small venous channels which gather blood from the region of the left portion of the greater curvature of the stomach ; they pass backwards towards the spleen, in the gastro-splenic ligament, and terminate either in the trunk of the splenic vein or in one of its main tributaries.

The left gastro-epiploic vein runs from right to left along the lower border of the stomach between the layers of the greater omentum. At the left extremity of the lower part of the greater curvature of the stomach it enters the gastro-splenic ligament, through which it passes towards the hilum of the spleen, and it terminates in the commencement of the splenic vein. It receives tributaries from both surfaces of the stomach.

The pancreatic veins issue from the substance of the pancreas, and terminate directly in the splenic vein.

The inferior mesenteric vein commences, as the superior hæmorrhoidal vein, in the venous plexus which lies between the muscular and mucous coats of the rectum. The superior hæmorrhoidal vein drains the greater part of the blood from the hæmorrhoidal plexus, through which it communicates with the middle and inferior hæmorrhoidal veins. It ascends, in company with the superior hæmorrhoidal artery and between the layers of the pelvic mesocolon,

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to the aperture of the pelvis minor, where it passes in front of the left common iliac artery and becomes the inferior mesenteric vein.

The inferior mesenteric vein runs upwards, on the left of the aorta, behind the peritoneum and in front of the left psoas major muscle and the left internal spermatic artery. Near its termination it crosses in front of the left renal vein, and, passing behind the body of the pancreas, ends in the splenic vein. Occasionally it terminates in the angle of union of the superior mesenteric and splenic veins.

Tributaries. In addition to the superior hæmorrhoidal vein, of which it is the direct continuation, the inferior mesenteric vein receives sigmoid tributaries from the iliac and pelvic colon, and the left colic vein from the descending colon and left colic flexure.

THE LYMPH VASCULAR SYSTEM.

vein

Thoracic duct

trunk

vein Left in nominate vein

Thoracic duct

The vessels of the lymph vascular system, vasa lymphatica, contain a colourless fluid, rich in white corpuscles, which is called lymph.

In many respects the lymph vessels resemble blood vessels, especially veins, and, like the veins, many of the

Right internal jugular vein lymph vessels, but not all, contain

Right jugular trunk

Broncho-mediastinal duct numerous valves, which control the

Left internal jugular vein direction of the circulation. Un- Right subclavian like the veins, however, the lymph Right subclavian

Left jugular trunk vessels communicate directly or

Left subclavian indirectly with the great serous cavities of

lymph trunk the body; and also unlike the veins, the

Left subclavian continuity of the lymph vessels is interrupted by interposed nodular aggregations of lymphoid tissue which are known as

Thoracic duct lymph glands.

Superior vena cava The corpusculated fluid called lymph, which fills the interiors of the lymph vessels, is partly collected from the serous cavities, and, in part, it passes into the lymph vessels from the surrounding tissues.

It is carried by the lymph vessels to the veins; for the smaller lymph vessels gradually unite together to form larger and larger channels until, ultimately, all the lymph passes into two main trunks—the thoracic duct, which terminates in the commencement of the left innominate vein, and the right lymph duct, which ends in the beginning of the right innominate vein. Obviously, therefore, all the lymph vessels

Cisterna chyli are afferent inasmuch as they carry the lymph owards the great central vessels, but it is

Left lumbar trunk customary to speak of some of the lymph vessels

Right lumbar trunk 8 vasa afferentia and others as vasa efferentia,

Intestinal lymph he former being vessels which carry lymph to ymph glands, and the latter, those which convey

- Testicular lymphatics he lymph from more peripheral towards more entral glands.

Lymph vessels from The lymph vessels merely collect and convey

pelvis

Lymph vessels from mph; the lymph glands probably serve in part

lower extremity s filters and in part as the sources of origin of ome of the lymph corpuscles, which are called mphocytes and which become white blood coruscles when they enter the blood stream.

Fig. 797.-DIAGRAM OF MAIN In its course from the tissues to the blood

LYMPH VESSELS. essels the greater part, if not the whole, of the mph passes through one and generally through more than one lymph gland. All parts of the body which possess blood-vessels, except the central nervous

vessels

system, the eye and the internal ear, are plentifully provided with lymph vessels which are divided, according to their positions, into superficial and deep vessels.

The superficial lymph vessels lie in the skin and subcutaneous tissues; they frequently accompany the superficial veins and, in the limbs, they join the deep vessels in definitely localised situations.

The deep lymph vessels drain the lymph from all parts of the body which lie internal to the deep fascia; they tend to accompany the blood- vessels of the various parts and organs.

The lymph glands also are divided into superficial and deep groups. The former lie in the superficial fascia and are comparatively few in number. Ther are associated more particularly with the superficial lymph vessels of the limle The deep lymph glands of the limbs are also comparatively few in number, but those of the head, neck, and trunk are very numerous.

Vasa Lymphatica. The smaller lymphatics are channels of various shapes but of greater calibre than the blood capillaries. They anastomose freely together, forming lymphatic plexuses.

Their walls are formed by a single layer of endothelial cells of irregular shape and sinuous outline, which are in close contact, externally, with the tissue elements amidst which they lie. In some cases lymph vessels, or plexuses of lymph vessels, surround the blood - vessels forming perivascular lymph channels. It has been generally believed that such perivascular channels are numerous in the central nervous system, but the researches of Bruce tend to show that, whilst the lymphocytes travel along the walls of the blood - vessels of the central nervous system, they pass along cleft-like spaces in the adventitial sheaths, and not in distinct perivascular channels.

As the lymph vessels attain a larger size their walls are strengthened by the deposition of a layer of elastic fibres on the outer surface of the endothelial coat The fibres run longitudinally, and in some cases fuse together to form a fenestrated elastic membrane.

The walls of all the largest lymph vessels, like those of the blood-vessels, are formed by three tunics, external, middle, and internal. The tunica intima consists of a layer of endothelium covered externally by elastic fibres or fenestrated elastie membrane. The tunica media is formed of transverse and oblique unstriped muscle fibres, intermingled with elastic fibres. The tunica externa consists of longitudina! connective tissue elements, with which are intermingled oblique and longitudinal unstriped muscle fibres; the latter feature being peculiarly characteristic, for it is not met with in the blood vascular system, except in the walls of the large veins.

Bicuspid valves, formed by semilunar folds of the tunica intima are extremely numerous in the lymph vascular system. They are either absent or they are few and incompletely developed in the small vessels and the lymph plexuses, but thes are very prevalent in the larger vessels ; consequently when the latter are injected they assume a modulated outline. Valves are present also at the entrances of the great lymph channels into the venous system.

Lymphoglandulæ.—Lymph glands are globular, ovoid, flattened, or irregular bodies, and each gland presents a localised depressed area which is known as the hilum. The lymph glands vary considerably in size, some being no larger than a pin’s-head, whilst others are as large as a bean. In colour they are usually grayish pink, but the tint varies with the position, vascularity, and state of activity of the gland. The lymph glands of the lung are generally blackened by the deposition of carbonaceous material in their substance, and those of the liver and spleen frequently have a brownish hue. The lymph glands of the mesentery are creamy or white whilst the chyle is rapidly passing through them, but when the absorption of food-material from the intestine ceases they become a rosy pink.

The lymph glands are embedded in the connective tissues, some lying superficially in the subcutaneous tissues, but the majority more deeply and usually at the sides of the great blood vessels. As a rule, they are arranged in groups of frote two to fifteen, but a few of those which lie in the subcutaneous tissues are solitary

They form centres to which afferent lymphatic vessels converge, and from which efferent vessels pass onwards to other glands or to the larger lymph channels

The student should, therefore, acquaint himself with the various groups of glands, with their afferents and efferents, and with the exact position and relations of the large lymphatic trunks; he will then be in a position to understand the course which minute organisms or particles, which have gained access to the lymph spaces, may take as they are carried in the lymph stream; and he will realise that such structures may either be entangled in the glands through which the lymph passes, or, having escaped all obstructions, that they will finally enter the veins at the roo of the neck. At the same time, if he bears in mind the existence of the numerous anastomoses between the lymph vessels, he will have no difficulty in appreciating that variations from any regular course may not infrequently occur, and his clinical experience at a later period will show that such variations are by no means uncommon.

Structure of Lymph Glands.-Lymph glands consist of (1) a skeleton or framework, (2) lymph sinuses, and (3) lymph follicles and cords; and each gland is separable into cortex and medulla. The cortex lies immediately internal to the capsule, except at the hilum, where it is absent. The medulla forms the internal part of the gland, and reaches the surface at the hilum.

(1) The skeleton or framework consists of a capsule and of primary, secondary, and tertiary trabeculæ

The capsule is formed of white fibrous tissue, interspersed with elastic fibres, and in some cases with unstriped muscular fibres.

The primary trabeculæ spring from the deep surface of the capsule and radiate through the cortex into the medulla. In the cortex they are flattened lamellæ, but as they reach the medulla they break up into flattened, rounded, and angular bands which unite freely together ; their structure is the same as that of the capsule, and from their surfaces the secondary trabeculæ are given off. The secondary trabeculæ spring from the surfaces of the primary trabeculæ, cross the lymph sinuses and enter the follicles of the cortex and the cords of the medulla, where they terminate by dividing into tertiary trabecula. As they cross the lymph sinuses they unite together freely, forming a fine mesh-work through which the lymph passes in its course from the afferent to the efferent vessels. The secondary trabeculæ consist of fine strands of fibrous tissue devoid of nuclei. The tertiary trabeculæ are finer and more delicate than the secondary trabeculæ, from the terminations of which they spring, but they have a similar structure. They unite together, forming a fine network in the lymph cords and follicles, and the spaces of the network are filled with lymph corpuscles. The surfaces of the trabeculæ which bound the lymph sinuses are covered with endothelial cells.1

(2) The lymph sinuses lie internal to the capsule and around the primary trabeculæ which form their boundaries on one side, whilst on the other they are limited by the lymph cords and follicles. They are traversed by the secondary trabeculæ, and their channels are thus converted into a kind of sponge-work through which the lymph stream flows. In the cortical parts of the glands they form more or less cylindrical channels, but in the medulla they become moniliforin. Afferent vessels enter the sinuses of the cortex, and the efferent vessels emerge from the medulla at the hilum.

The lymph follicles lie in the cortical portions of the lymph glands, where they form the inner boundaries of the lymph sinuses. They consist of dense masses of lymphoid cells, embedded in a stroma formed by the tertiary trabeculæ, and they are continuous internally with the lymph cords of the medullary substance.

The lymph cords are continuous with the lymph follicles, and have the same structure, but they lie in the medullary portions of the glands; they are cord-like and not nodular in shape, and they form the peripheral boundaries of the lymph sinuses of the medulla.

The Blood-Vessels of the Lymph Glands. - Blood-vessels are distributed to the capsule and through the capsule to the primary trabeculæ of the glands; but the main blood vessels to each gland enter the hilum and ramify in the lymph cords and follicles, amidst the tertiary trabeculæ which are connected with the walls of the vessels.

Hæmal Lymph Glands.—In various parts of the body, but more particularly in the retro-peritoneal region, and especially along the line of the abdominal aorta, a number of bodies may be found which have all the ordinary structural characters of lymph glands, but they differ from lymph glands inasmuch as some of their sinuses contain blood. These structures are called hæmal lymph glands. The sinuses of the hæmal lymph glands which contain lymph are in continuity with lymphatics, whilst the blood-filled sinuses open into blood vessels. It is stated that communications exist between the blood and the lymph containing sinuses of the hæmal lymph glands, but the evidence on this point is not quite satisfactory.

Hæmal Glands.—The term “ hæmal gland” is applied to nodules possessing the structure of ordinary lymph glands, but which contain only blood in their sinuses; they probably belong, however, as their development shows, to the lymph vascular and not to the blood vascular system (see p. 1042). 1 See p. 1059.

THE TERMINAL LYMPH VESSELS. The terminal lymph vessels are the thoracic duct and the right lymphatic duct.

Ductus Thoracicus. — The thoracic duct is by far the larger and the longer of the two terminal lymph vessels. It commences, in the epigastric region of

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the abdomen, as an elongated ovoid dilation—the cisterna chyli—which measures 6 to 8 mm. (1 to } in.) in its broadest diameter, and from 50 to 75 mm. (2 to 3 in.) in length. cisterna chyli lies between the aorta and the lower part of the vena azygos, posterior to the right crus of the diaphragm, and opposite the first and second lumbar vertebræ. Passing upwards from the cisterna, the thoracic duct traverses the aortic opening of the diaphragm and enters the posterior

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