AN ANOMALY OF THE THORACIC DUCT. f)l 



stream of ducts leads to the left iliac nodes. The large node already referred to, which lies 

 ventral to the aorta near its bifurcation, receives (in addition to the vessels mentioned) 

 ducts from the vessels accompanying the inferior mesenteric artery. 



In brief, then, the conditions present are these: The thoracic duct is rudimentary; it 

 occupies its normal position, but extends posteriorly only as far as the body of the ninth 

 vertebra, where it starts as a small vessel draining the ninth intercostal space. The dorsal 

 body wall posterior to the ninth intercostal space, the abdominal and pelvic viscera, and 

 both posterior extremities are drained by vessels which collect into a large duct which starts 

 in the region of the anterior iliac lymph nodes opposite the last lumbar vertebra, runs pos- 

 teriorly beneath the ligamentum inguinale, hooks around the terminal bend of the great 

 saphenous vein, and then courses anteriorly in the superficial fascia over the ligamentum 

 inguinale, over the lateral abdominal and thoracic wall, through the axilla, and into the left 

 subclavian vein near its juncture with the internal jugular. 



Associated with this condition is a variation of the hemiazygos and left renal veins, 

 significant features of which are: (1) the veins draining the left intercostal spaces, below 

 the third, collect into a vein which crosses to the right ventral to the aorta, at the level of 

 the ninth thoracic vertebra, to join the main azygos, and this cross branch lies between 

 the lower end of the thoracic duct and the most anterior loop of the abdominal lymphatics; 

 (2) there is a considerable anastomosis between the hemiazygos and the left renal which, 

 in turn, runs posteriorly to join the inferior vena cava at its point of formation by the 

 junction of the two iliac veins. 



So far as I have been able to learn, no such abnormality of the lymphatic system has 

 been described. 



While any explanation of this condition must necessarily be mainly speculative, certain 

 facts, in connection with our knowledge of the mode of development of lymphatics, are 

 suggestive. First, it should be noted that there is no evidence of any pathological condi- 

 tion in the region where the thoracic duct ends. Turning then to the embryo, it has been 

 shown by Miss Sabin (1, 1913, 63) that, in pig embryos, valves begin to develop in lym- 

 phatic vessels in embryos of 7 cm. Thus, she was able, in embryos of 5.5 cm. (2, 1904, 86), 

 by inserting the injecting needle into the dermis at any point, to inject the entire network 

 of subcutaneous lymphatics, which form, at this stage, a richly anastomosing network over 

 the body wall. In human embryos Miss Sabin (3, 1912, 728) found that valves apparently 

 begin to develop in the larger vessels of the subcutaneous network in embryos of 5.5 cm. 

 For a considerable time previous to the development of valves, the body-wall plexus 

 collects anteriorly into ducts which pass into the axillary region, posteriorly into ducts 

 which pass into the depth in the inguinal region, and which eventually reach the recep- 

 taculum. Polinski (4, 1910) has demonstrated, in bovine embryos, a temporary lateral 

 vessel which differentiates in the midst of the plexus in the lateral body wall. Mierzejewski 

 (5, 1909) has found in chick embryos a transitory longitudinal vessel in the body wall 

 which runs from the axilla along the lateral body wall over the pelvic region. Mrs. E. L. 

 Clark, in a series of observations, soon to be published, and which she kindly permits me 

 to refer to, on the circulatory conditions in the superficial lymphatics of living chicks, finds 

 that the circulation in lymphatics starts very gradually and that, in early stages, slight 

 disturbances may result in a complete reversal of the direction of lymph flow. Obviously, 

 then, since there is a considerable period in which no valves are present, there is the possi- 

 bility that were there any unusual condition which should offer a sufficient resistance to 

 the flow of lymph through the thoracic duct, the lymph might make its way posteriorly in 



