64 Florence B. Sabin. 



surface of the Wolffian bodies and supplies their capsule as well a 

 the reproductive glands. From the sac vessels grow to the stomacl 

 and the entire intestine, including the rectum. The lymphatics o 

 the diaphragm can be injected from the retroperitoneal sac. The de 

 velopment of the lymphatics of the diaphragm, liver, capsule of th 

 spleen, adrenal and pancreas has not yet been worked out. 



Heuer (43) has followed the lymphatics of the intestine from th 

 retroperitoneal sac to the ultimate lacteals. While the embryo ii 

 growing from 3 to 4 cm. long a very abundant plexus of eapillarie: 

 spreads out in the mesentery. The lymphatics reach the wall of th< 

 intestine by the time the embryo is 4 cm. long. They first enter th< 

 submucosa and form then a primary plexus. Heuer's figures 9 anc 

 10 show that the early vessels in the submucosa have a segmenta 

 arrangement, which is, however, nearly lost as the complete plexus 

 forms. The plexus of the mucosa, and of the serosa are both second- 

 ary. The lacteals develop from the mucosal plexus and are presem 

 in a pig measuring 9 cm. The mesenteric vessels and the submucosa. 

 plexus develop valves. 



. The iliac lymphatics and the thoracic duct : The lymphatics whicl 

 arise from the mesonephritic veins on the two sides form a verj 

 simple pattern. Starting from the veins at the hilus of the twc 

 Wolffian bodies they grow caudalward along the edge of the Wolffiar 

 bodies to make the iliac sacs, and cerebralward along the dorsal sur- 

 face of the aorta to form the cisterna chyli. The lymphatics dorsad 

 to the aorta grow in two directions: (1) caudalward to form a chair 

 of prevertebral lymph nodes and (2) cerebralward to form the thoracic 

 duct. 



The iliac lymphatic sacs are two long symmetrical sacs extending 

 from the hilus of the Wolffian bodies to the level of the bifurcatior 

 of the aorta. In an embryo 23 mm. long they drain into the mesone- 

 phritic veins. By the time theembryo is 25 to 27 mm. long this 

 connection is lost and the two iliac sacs converge into the median 

 cisterna chyli dorsal to the aorta. 



The caudal end of the iliac lymphatics in the pig is a sac of con- 

 siderable size, from which three sets of lymphatics can be injected 

 the ilio-lumbar, the femoral and a plexus which surround the umbil- 

 ical arteries. The ilio-lumbar superficial lymphatics are very con- 

 spicuous in the pig, as shown in figs. 4 and 5 (Sabin 130). This is in 

 marked contrast to the human embryo, where they form part of the 

 inguinal group. 



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