The Lymphatic System in Human Embryos, 75 



terior lymph sac on the other, making a definite indication of the pos- 

 terior lymphatic sacs. This stage is, I believe, just preliminary to the 

 formation of the three abdominal sacs. In the next specimen these 

 sacs become definite. 



Thus in the first fourteen specimens of the series, measuring from 

 8 to 20 mm., simply the jugular sacs are present. From now on, 

 that is in embryos above 20 mm., we shall have to follow not only 

 the jugular sacs but the mesenteric sac, the cistema chyli and the 

 posterior' lymph sacs as well. 



The first embryo above 20 mm. in the series, is one (No. 382) 

 measuring 23 mm. This series is cut in sagittal sections. It shows 

 the jugular sac beautifully, which has now reached a size of 2 x 1 

 mm., and lies opposite the third, fourth and fifth cervical vertebrae. 

 The series, however, is much more important in connection with the 

 other lymphatic sacs. I cannot find the posterior lymph sac, but both 

 the mesenteric sac and the cisterna chyli are present. For these two 

 median sacs the sagittal plane proves to be by far the best. In Fig. 

 11, which was made by graphic reconstruction, is shown the retro- 

 peritoneal sac in its relation to the renal vein and the suprarenal body. 

 It is designed to relate the mesenteric sac and cisterna chyli to the 

 surrounding structures. The point at which the vena cava turns 

 ventralward, opposite the second lumbar vertebra, marks the position 

 both of the renal veins and also the suprarenal branch which is a 

 large vein running anteriorly along the ventral surface of the supra- 

 renal body. The retroperitoneal sac extends along the renal and 

 suprarenal veins, the latter being hidden in the diagram by the vena< 

 ■cava. In following the suprarenal veins the lymphatic vessels ap- 

 proach the superior mesenteric artery, along which they subsequently 

 grow out into the mesentery, as has been shown by Heuer.^^ The 

 line of mesentery is shoAvn in the diagram. The diagram shows the 

 mass of sympathetic ganglia closely related to the suprarenal body. 

 In this early stage the lymphatic ducts, are not likely to be confused 

 with the sympathetic ganglia, but later when nodes begin to develop 

 •care must be exercised to distinguish them. The diagram also shows 



^'Heuer. Amer. Jour. Anat, Vol. IX, No. 1. 



