■■■'■- /,'. Sabin. 



dothelium is best broughl out by total mounts of silver nitrate in- 



or the retroperitoneal Bac in the pig. 

 When the prima are thus completely bridged by these bands 



are practically a dense plexus of lymphatic capillaries and are 

 therefore in the firsl praenl of lymph glands. A.I 



this - connective tissue Bepta are undifferentiated and contain 



only in. sen< bj me and blood capillai 



We arc now in a position to consider the question of which 



lymph nodes in the embryo. This point has been discussed by 

 Lewis (77) and Sabin (131 and L34). Ii depends on the criterion 



[f th criterion is recognizing the formation of a pies 

 lymphatic capillaries with undifferentiated connective tissue bi 



e anlagen of a gland, then it is clear that the primary lymph 

 glands, that i-. those that come from the lymph sacs, are the 



rlands to begin for each region of the body. Thus the jugular- 

 subcli 3ac in tin' human embryo i- . ■ ed at 30 mm. 



and is therefore a plexus of lymphatics, the anlage of a lymph gland. 

 A.t tl i we are agi re are do lymphocytes (Kling (72), 



Lewis ind Sabin i 13] | i. If. on t! ther hand, the crrl 



pment of the first lymphocytes in the body, we must 

 say that this point lias not been reii e all the primary 



embryo have been determined. Saxer | L38, 

 !'■ :;< 1) notes that lymph nodes arc lK-ginning in the neck, the 

 terior mediastinum, the retroperitoneal outside of both 



and along the Wolffian bodies in bovine embryos 4.5 cm. long, 

 «i«<l in shi the same length describes in wander- 



in the same areas. Kling (72) has no specimens of human 

 embryo between 3] mm., where, he says, then- are no lymphocytes in 

 -i!lar\ glands, ami ]n ni.. when lymphocytes .ire present in many 

 glands. Lewi- (',;) finds lymp in human embryos 42 mm. 



I' 1 ' finds that they occur practically simultaneously in the 

 glands around the internal jugular vein (primary lymph m 

 and certain " isolated subcutaneous lymph -land-.'" of which he figun - 

 one or two along the linguo-facial vein and its branches. The relation 

 "I' tl • [ids to lymphatic vessels will he readily made out by a 



-nel fig. 16. Figure 8 shows the ducts from the 

 th" linguo-facial vein at a Btage even younger than Lewis's 

 isolated glands, namely, a pig measuring •"..•"> cm. Moreover the be- 

 ginning cervical plexus from which these submaxillary vessels come 



