Page:EB1911 - Volume 17.djvu/182

Rh aortic glands are grouped all round the length of the aorta, and are divided into pre-, retro- and lateral aortic groups (fig. 2 P.A. and L), all of which communicate freely. The upper preaortic glands are massed round the coeliac axis, and receive afferents from the gastric, hepatic, splenic and pancreatic glands; they are known as coeliac glands. The lateral aortic glands drain the kidney, adrenal, testis, ovary, fundus of uterus and lateral abdominal walls. In the upper extremity a few small glands are sometimes found near the deep arteries of the forearm. At the bend of the elbow are the ante-cubital glands (fig. 1 ) and just above the internal condyle, one or two supra-trochlear glands (fig. 1, ). The axillary glands (fig. 1, ) are perhaps the most practically important in the body. They are divided into four sets: (1) external, along the axillary vessels, draining the greater part of the arm; (2) anterior, behind the lower border of the pectoralis major muscle, draining the surface of the thorax including the breast and upper part of the abdomen; (3) posterior along the subscapular artery, draining the back and side of the trunk as low as the umbilical zone; (4) superior or infra-clavicular glands (fig. 1, ), receiving the efferents of the former groups as well as lymphatics accompanying the cephalic vein. In the lower limb all the superficial lymphatics pass up to the groin, where there are two sets of glands arranged like a T. The superficial femoral glands (fig. 1, ) are the vertical ones, and are grouped round the internal saphenous vein; they are very large, drain the surface of the leg, and are usually in two parallel rows. The inguinal glands form the cross bar of the T (fig. 1, ), and drain part of the buttock, the surface of the abdomen below the umbilicus and the surface of the genital organs. The deep lymphatics of the leg drain into the anterior tibial gland on that artery, the popliteal glands in that space, and the deep femoral glands surrounding the common femoral vein.

The thoracic duct begins as an irregular dilatation known as the receptaculum chyli, opposite the first and second lumbar vertebrae, which receives all the abdominal lymphatics as well as those of the lower intercostal spaces. The duct runs up on the right of the aorta through the posterior mediastinum and then traverses the superior mediastinum to the left of the oesophagus. At the root of the neck it receives the lymphatics of the left arm and left side of the neck and opens into the beginning of the left innominate vein, usually by more than one opening.

The right lymphatic duct collects the lymphatics from the right side of the neck and thorax, the right arm, right lung, right side of the heart and upper surface of the liver; it is often represented by several ducts which open separately into the right innominate vein.

Haemolymph glands are structures which have only been noticed since 1884. They differ from lymphatic glands in their much greater vascularity. They assist the spleen in the destruction of red blood corpuscles, and probably explain or help to explain the fact that the spleen can be removed without ill effects. In man they extend along the vertebral column from the coeliac axis to the pelvis, but are specially numerous close to the renal arteries.

T. Lewis suggests that lymphatic and haemolymph glands should be classified in the following way:—

Details and references will be found in papers by T. Lewis, ''J. Anat. & Phys.'' vol. xxxviii. p. 312; W. B. Drummond, ''Journ. Anat. and Phys.'' vol. xxxiv. p. 198; A. S. Warthin, ''Journ. Med. Research, 1901, p. 3, and H. Dayton, Am. Journ.'' ''of Med. Sciences'', 1904, p. 448. For further details of man’s lymphatic system see The Lymphatics by Delamere, Poirier and Cuneo, translated by C. H. Leaf (London, 1903).

Embryology.—The lymphatic vessels are possibly developed by the hollowing out of mesenchyme cells in the same way that the arteries are; these cells subsequently coalesce and form tubes (see ). There is, however, a good deal of evidence to show that they are originally offshoots of the venous system, and that their permanent openings into the veins are either their primary points of communication or are secondarily acquired. The lymphatic and haemolymph glands are probably formed by the proliferation of lymphocytes around networks of lymphatic vessels; the dividing lymphocytes form the lymphoid tissue, and eventually the network breaks up to form distinct glands into which blood vessels penetrate. If the blood vessels enlarge more than the lymphatic, haemolymph glands result, but if the lymphatic vessels become predominant ordinary lymphatic glands are formed. At an early stage in the embryo pig two thoracic ducts are formed, one on either side of the aorta, and the incomplete fusion of these may account for the division often found in man’s duct. In the embryo pig too there have been found two pairs of lymph hearts for a short period.

See A. S. Warthin, ''Journ. Med. Research'', vol. vii. p. 435; F. R. Sabin, ''Am. Journ. of Anat.'' i., 1902; and, for literature, Development of the Human Body, by J. P. McMurrich (London, 1906), and Quain’s Anatomy (vol. i., London, 1908).

Comparative Anatomy.—A lymphatic system is recognized in all the Craniata, and in the lower forms (fishes and Amphibia) it consists chiefly of lymph spaces and sinuses in communication with the coelom. In fishes, for instance, there is a large subvertebral lymph sinus surrounding the aorta and another within the spinal canal. In Amphibia the subvertebral sinus is also found, and in the Anura (frogs and toads) there is a great subcutaneous lymph sinus. Lymph hearts are muscular dilatations of vessels and are found in fishes, amphibians, reptiles and bird embryos, and drive the lymph into the veins; they are not known in adult mammals.

In birds the thoracic duct is first recognized, and opens into both right and left precaval veins, as it always does in some mammals. In birds, however, some of the lymphatics open into the sacral veins, and it is doubtful whether true lymphatic glands ever occur. In birds and mammals lymphatic vessels become more definite and numerous and are provided with valves.