The Vena azygos minor commences in the lumbar region, on the left side, by a communication with one of the lumbar veins or with the renal vein. It enters the chest through the left crus of the diaphragm and ascends the left side of the vertebral column, crosses the fifth or sixth dorsal vertebra and opens into the vena azygos major. It receives the six or seven lower intercostal veins of the left side. The azygos veins have no valves. The Right superior intercostal vein receives the veins of the first and second intercostal space, and opens into the subclavian vein of the same side. The Left superior intercostal vein is the trunk formed by the union of the five or six upper intercostal veins of the left side. It communicates below with the vena azygos minor, and crosses the arch of the aorta to terminate in the left vena innominata. It receives the left bronchial vein. VERTEBRAL AND SPINAL VEINS. The numerous venous plexuses of the vertebral column and spinal cord may be arranged into three groups : Dorsi-spinal, Meningo-rachidian, Medulli-spinal. The Dorsi-spinal veins form a plexus around the spinous, transverse, and ar ticular processes, and arches of the vertebræ. They receive the returning blood from the dorsal muscles and surrounding structures, and transmit it, in part to the meningo-rachidian, and in part to the vertebral, intercostal, lumbar, and sacral veins. The Meningo-rachidian veins are situated between the dura mater spinalis and the vertebræ. They communicate freely with each other by means of a complicated plexus. In front they form two longitudinal trunks (longitudinal spinal sinuses), extending the whole length of the column on each side of the posterior common ligament, and are joined on the body of each vertebra by transverse trunks, which pass beneath the ligament, and receive the large basi vertebral veins from the interior of each vertebra. The meningo-rachidian veins communicate superiorly through the anterior condyloid foramina with the internal jugulars; in the neck they pour their blood into the vertebral veins; in the thorax, into the intercostals; and in the loins and pelvis into the lumbar and sacral veins, the communications being made through the intervertebral foramina. The Medulli-spinal veins are situated between the pia mater and arachnoid; they communicate freely with each other to form plexuses; and send branches through the intervertebral foramina with each of the spinal nerves, to join the veins of the trunk. CARDIAC VEINS. The veins (cardiacæ vel coronaria cordis) returning the blood from the substance of the heart are, the Great cardiac vein, Anterior cardiac veins, The Great cardiac vein (vena cordis magna; coronaria magna) commences st the apex of the heart, and ascends along the anterior ventricular groove to the base of the ventricles; it then curves around the left auriculo-ventricular groove to the posterior part of the heart, where it terminates in the right auricle. It receives in its course the left cardiac veins from the left auricle and ventricle, and the posterior cardiac veins from the posterior ventricular groove. The Posterior cardiac vein (vena cordis media), frequently two in number, commences also at the apex of the heart, and ascends along the posterior ven tricular groove, to terminate in the great cardiac vein. It receives the veins at right angles from the posterior aspect of the two ventricles The Anterior cardiac veins (venæ parvæ), collect the blood from the anterior surface of the right ventricle; one larger than the rest runs along the right border of the heart and joins the trunk formed by these veins, which curves around the right auriculo-ventricular groove, to terminate in the great cardiac vein near its entrance into the right auricle; others cross the groove, and open directly into the auricle. The Vena Thebesii (venæ minima) are numerous minute venules which convey the venous blood directly from the substance of the heart into the right auricle. The cardiac veins have no valves, excepting that at the orifice of the great vein. The portal system is composed of four large veins which return the blood from the chylopoietic viscera; they are the The Inferior mesenteric vein receives its blood from the rectum by means of the hæmorrhoidal veins, and from the sigmoid flexure and descending colon, and FIG. 233. THE PORTAL VEIN. 1. Inferior mesenteric vein; it is traced by means of dotted lines behind the pancreas (2) to terminate in the splenic vein (3). 4. Spleen. 5. Gastric veins, opening into the splenic vein. 6. Superior mesenteric vein. 7. Descending portion of the duodenum. 8. Its transverse portion, crossed by the superior mesenteric vein and part of the trunk of the superior mesenteric artery. 9. Portal vein. 10. Hepatic artery. 11. Ductus communis choledochus. 12. Division of the duct and vessels at the transverse fissure of the liver. 13. Cystic duct leading to the gall-bladder. ascends behind the transverse duodenum and pancreas, to terminate in the splenic vein. Its hæmorrhoidal branches inosculate with branches of the internal iliac vein, and thus establish a communication between the portal and general venous system. The Superior mesenteric vein is formed by branches which collect the venous blood from the capillaries of the superior mesenteric artery; they constitute by their junction a large trunk, which ascends by the side of the corresponding artery, crosses the transverse portion of the duodenum, and unites behind the pancreas with the splenic in the formation of the portal vein. The Splenic vein commences in the structure of the spleen, and quits that organ by several large branches; it is larger than the splenic artery, and perfectly straight in its course. It passes horizontally inwards behind the pancreas, and terminates near its greater end by uniting with the superior mesenteric and forming the portal vein. It receives in its course the gastric and pancreatic veins, and near its termination the inferior mesenteric vein. The Gastric veins correspond with the gastric, gastro-epiploic, and vasa brevia arteries, and terminate in the splenic vein. The VENA PORTE, formed by the union of the splenic and superior mesenteric vein behind the pancreas, ascends through the right border of the lesser omentum to the transverse fissure of the liver, where it divides into two branches, one for each lateral lobe. In the right border of the lesser omentum it is situated behind and between the hepatic artery, and ductus communis choledochus, and is surrounded by the hepatic plexus of nerves and lymphatics. At the transverse fissure each primary branch divides into numerous secondary branches which ramify through the portal canals, and give off vaginal and interlobular veins, and the latter terminate in the lobular venous plexus of the lobules of the liver. The portal vein within the liver receives the venous blood from the capillaries of the hepatic artery. PULMONARY VEINS. The pulmonary veins (venæ pulmonales), four in number, return the arterial blood from the lungs to the left auricle of the heart; they differ from veins in general, in the area of their cylinders being but little larger than that of the corresponding arteries, and in accompanying singly each branch of the pulmonary artery. They commence in the capillaries upon the parietes of the intercellular passages and air-cells, and unite to form a single trunk for each lobe. The vein of the middle lobe of the right lung unites with the superior vein, so as to form the two trunks which open into the left auricle. Sometimes they remain separate, and then there are three pulmonary veins on the right side. The right pulmonary veins behind pass behind the right auricle to the left auricle; the left pass in front of the descending aorta; they both pierce the pericardium. Within the lung the branches of the pulmonary veins are behind the bronchial tubes, and those of the pulmonary artery in front; but at the root of the lungs the veins are in front, next the arteries, and then the bronchi. There are no valves in the pulmonary veins. CHAPTER VIII. OF THE LYMPHATICS. THE lymphatic vessels, or absorbents, have received their double appellation from certain phenomena which they present; the former name being derived from the appearance of the limpid fluid (lympha, water) which they convey; the latter from their supposed property of absorbing foreign substances into the system. They are minute, delicate, and transparent vessels, remarkable for their general uniformity of size, a knotted appearance which is due to the presence of numerous valves, their frequent dichotomous divisions, and their division into several branches immediately before entering a gland. Their office is to collect the products of digestion and the detrita of nutrition, and convey them into the venous circulation near the heart. [FIG. 234. Lymphatic vessels commence in a delicate network which is distributed in the cutaneous surface of the body, on the various surfaces of organs, and throughout their internal structure; and from this network the lymphatic vessels proceed, nearly in straight lines, in a direction towards the root of the neck. In their course they are intercepted by numerous small, spheroid or oblong, or flattened bodies, lymphatic glands. The lymphatic vessels entering these glands are termed vasa inferentia or afferentia, and those which quit them, vasa efferentia. The vasa inferentia vary in number from two to six, they divide at the distance of a few lines from the gland into several smaller vessels, and enter it by one of its flattened surfaces. The vasa efferentia escape from the gland at the opposite, but not unfrequently on the same surface; they consist, like the vasa inferentia at their junction with the gland, of several small vessels which unite after a course of a few lines to form from one to three trunks, often double the size of the vasa inferentia. Lymphatic Vessels admit of a threefold division, into superficial, deep, and lacteals. LYMPHATIC VESSELS OF THE SKIN OF THE BREAST injected; after Breschet. a. Superficial plexus. b. Deeper plexus. c. Alymphatic vessel, which proceeded to the axillary glands.] The Superficial lymphatic vessels, on the surface of the body, follow the course of the veins, and pierce the deep fascia in convenient situations, to join the deep lymphatics. On the surface of organs they converge to the nearest lymphatic trunks. The superficial lymphatic glands are placed in the most protected situations of the superficial fascia, as in the hollow of the ham and groin in the lower extremity; on the inner side of the arm in the upper extremity. The Deep lymphatics, fewer in number and somewhat larger than the superficial vessels, accompany the deeper veins; those from the lower parts of the body converging to the numerous glands seated around the iliac veins and inferior vena cava, and terminating in a large trunk situated on the vertebral column, the thoracic duct. From the upper part of the trunk of the body on the left side, and from the left side of the head and neck, they also proceed to the thoracic duct. Those on the right side of the head and neck, right upper extremity, and right side of the thorax, form a distinct duct [ductus lymphaticus dexter which terminates at the point of junction of the subclavian with the internal jugular vein on the right side of the root of the neck. 1 See Mr. Lane's article on the "Lymphatic System," in the Cyclopædia of Anatomy and Physiology. The Lacteals are the lymphatic vessels of the small intestines; they have received their distinctive appellation from conveying the milk-like product of digestion, the chyle, to the great centre of the lymphatic system, the thoracic duct. They are situated in the mesentery, and open into the numerous mesenteric glands in their course. Lymphatic vessels are very generally distributed through the animal tissues; there are, nevertheless, certain structures in which they have not been detected; for example, the brain and spinal cord, the eye, bones, cartilages, tendons, the membranes of the ovum, umbilical cord, and placenta. Anastomoses between these vessels are less frequent than between arteries, and veins; they are effected by means of vessels of equal size with the vessels which they connect, and no increase of calibre results from their junction. The lymphatic vessels are smallest in the neck, larger in the upper extremities, and larger still in the lower limbs. For the purpose of effecting the movement of their fluids in a proper direction, lymphatic vessels are furnished with valves, and it is to these that the appearance of constrictions around the cylinders of the vessels, at short distances, is due. Like the valves of veins, the valves of lymphatic vessels are each composed of two semilunar flaps attached by their convex border to the sides of the LYMPHATIC GLAND AND VESSELS. A. One of the inguinal lymphatic glands injected with mercury; a, afferent lymphatic vessels from the lower extremity; b, efferent vesselsothers are also seen. B. One of the superficial lymphatic trunks of the thigh. c. One of the femoral lymphatic trunks laid open longitudinally to display the valves within it; c, sinus between the flap of the valve and the wall of the vessel. d. Surface of one flap directed towards the opposite; e, semicircular attached margin of the flap.] vessel and free by their concave border. This is the general character of the valves, but, as in veins, there are exceptions in their form and disposition; sometimes one flap is so small as to be merely rudimentary, while the other is large in proportion; sometimes the flap runs all the way round the tube, leaving a central aperture, which can only be closed by a contractile power in the valve |