The Origin and Development of the Lymphatic System. 67 



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

 [and. 'From the cerebral end of the plexus vessels are forming a 

 land at the point where the lymphatics divide to form the facial and 

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



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

 8 there is a developing submaxillary lymph gland along the course 

 E the facial branch of the linguo-facial vein (fig. 8) . The small facial 

 ode and the submaxillary node are tertiary nodes compared with the 

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

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

 jcondary and tertiary nodes are constant in the pig. 



The mesenteric glands are secondary for the retroperitoneal sac. 

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

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

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

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

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

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



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

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

 lands develop to the leg, the ventral abdominal wall and the external 

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

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

 lands opposite the bifurcation of the aorta. 



The histological development of lymph glands is now well under- 

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

 rimarily the development of lymphocytes which I shall not attempt 

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

 land as a whole. Prom the time of Breschet (16) it has been known 

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

 dopment 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- 

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

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

 meal sac these bands are never absent (figs. 498 and 499, Sabin 134). 

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

 >ng m fig. 495 (Sabin 134). That these bridges are entirely covered 



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