The largest absorbent glands of the thoracic cavity are those which receive the lymphatics from the lungs; they are situated at the roots of the lungs, pretty closely attached to the bronchi; they are generally of a dark colour and are called bronchial glands. Those asso ciated with the lymphatic vessels of the heart are few and small ; two or three may generally be noticed of the size of millet-seeds on the aorta and pulmonary artery, where these vessels are invested by the pericardium. In the poste rior mediastinum close to the thoracic duct three or four large lymphatic glands are usually met with, as well as several smaller ones in the intercostal spaces, not far from the thoracic duct. In the anterior mediastinum also some small glands may be observed imbedded in loose cellular tissue in the neighbourhood of the internal mammary vessels. Occasionally a small gland may be seen on the convex sur face of the diaphragm.
In the substance or parenchyma of the dif ferent. organs no lymphatic glands have been detected. They have never been seen in the brain, spinal marrow, in the lungs, liver, spleen, kidney, or testicles, in nerve, muscle, or bone.
Having given this general outline of the position of the lymphatic glands, I shall now proceed to describe the trunks of the system.
The thoracic duct, (fig. .53,) or principal trunk of the lymphatic system, generally com mences on the 'body of the second lumbar vertebra pretty exactly in the median line, concealed behind the root of the right ermil gent artery, bounded on the right by the right erns of the diaphragm, and to the left by the aorta, towhich it is connected by cellular tissue. It may be said to be formed by the union of the lymphatics of the lower extremities with the trunks of the lactcals proceeding from the intestines. At the conflux of the principal vessels from these three sources,—and there may be more than one from each,—a dilatation is sometimes found, which has been called the receptaculum chyli. From the body of the se cond lumbar vertebra the thoracic duct ascends into the thorax between the aorta and vena azygos. In the thorax it is situated behind the right pleural fold of the posterior medias ....
I tirium, having the aorta to its left, the vena azygos to its right, and the cesopliagus in front. In this position it ascends as high as the fourth or third dorsal vertebra, at which level, con tinuing its course upwards, it turns from right to left, passing behind the descending portion of the arch of the aorta, above which it ap pears a little external to the root of the left subclavian artery, from whence continuing to ascend it passes between the latter and the left common carotid artery, lying on the longus colli muscle; it now mounts into the cervical region in front of the vertebral artery and vein to the level of the seventh cervical vertebra, opposite to which it begins to form a curve, first forwards and outwards, then down wards and inwards, striding over the subclavian artery to reach the angle of union between the subclavian and internal jugular veins, at which point it empties itself into the venous system either by one or more branches.
The thoracic duct is not uniform in diameter throughout its course ; besides the occasional dilatation at its commencement, it generally presents another on the fourth dorsal vertebra just below its passage behind the descending thoracic aorta. Its narrowest part usually cor responds to the sixth or seventh dorsal vertebra. The duct is frequently tortuous and rarely single throughout. It often splits into two or more branches, which after a longer or shorter course reunite; this division and reunion may be two or three times repeated, and it may ul timately terminate by two or three branches instead of one.
The principal irregularities in the arrange ment of the thoracic duct, which have been recorded by anatomists, are— a doublebduct, one terminating in the left, the other in the right side of the neck ; a bifurcation of the duct at a higher or lower level, one branch terminating in the angle of union of the subclavian and internal jugular veins of the left side, the other emptying itself either into the corresponding point on the right side or joining the right lymphatic trunk, close to its termination ; a single trunk terminating altogether on the right side of the conflux of the internal jugular and subclavian veins, in which case a short lym phatic trunk is found on the left side similar to that which usually exists on the right, con stituting a partial lateral inversion or trans position confined to the trunks of the lymphatic system.
Besides the lymphatics of the lower extre mities and the lacteals, the thoracic duct re ceives directly or indirectly the lymphatics of the remaining abdominal viscera (except a few from the right lobe of the liver), those from the exterior and interior of the lower half of the trunk ; also the lymphatics of the left upper extremity, and left side of the head and neck, those from the left lung, the left side of the heart, and from the exterior and interior of the left upper half of the body.