The Origin and Development of tin' Lymphatic System. 6' 



jugular vein. In fig. 17 this plexus is shown as one large lymph 

 gland. From the cerebral end of the plexus vessels are forming a 

 gland al the point where the lymphatics divide to form the facial and 

 the temporal lymphatics. The cervical plexus in the adult pig becomes 

 a group of at least a dozen small lymph glands. In both figs. 17 and 

 18 there is a developing submaxillary lymph gland along the course 

 of the facial branch of the linguo-facial vein (fig. 8). The small fa< ial 

 node and the submaxillary node are tertiary nodes compared with the 

 jugular lymph sac. They show how lymph glands develop at points 

 where lymph ducts radiate out on their development. The primary, 

 secondary and tertiary nodes are constant in the pig. 



The mesenteric glands are secondary for the retroperitoneal sac. 

 The secondary glands from the iliac sac are very simple, for there are 

 only two of them: (1) The ileo-inguinal gland, which is very charac- 

 teristic of the pig and which remains as a single gland. Its position 

 is readily made out in fig. 4 (Sabin 130), for the superficial lymphatics 

 of the posterior body wall radiate to it. Like the superficial cervical 

 glands it is superficial. (2) The inguinal glands in the pig become 

 a large group of superficial glands, the position of which can be made 

 out in fig. 5 (Sabin 130). The lymph ducts from the inguinal lymph 

 glands develop to the leg, the ventral abdomiiral wall and the external 

 genital organs. The efferent vessels of the inguinal group of glands 

 and ileo-inguinal gland converge to the large group of primary iliac 

 glands opposite the bifurcation of the aorta. 



The histological development of lymph glands is now well under- 

 stood. The work of Saxer (138) on developing lymph glands considers 

 primarily the development of lymphocytes which I shall not attempt 

 to discuss in this paper, confining the work to the development of the 

 gland as a whole. From the time of Breschet (16) it has been known 

 that lymph glands begin as a plexus of lymphatic ducts. Their de- 

 velopment can be followed through the work of Ranvier (117), Bartels 

 (10). Gulland (39), Kling (72), Jolly (59), Lewis (77), and Sabin 

 (131). 



The primary lymph glands, which, with the exception of the post- 

 aortic, develop out of sacs, begin by a bridging of the sac by bands of 

 connective tissue covered by endothelium. In the case of the retroperi- 

 toneal sac these bands are never absent (figs. 498 and 409, Sabin 13 1 ). 

 For the jugular lymph sac they show well in human embryo 30 mm. 

 long in fig. 495 (Sabin 134). That these bridges are entirely covered 



