38 



Frederic T. Lewis. 



cles, and appears to communicate witli the vein bv a slender oblique 

 passage which is completely filled by a single file of blood 

 corpuscles. This lymphatic space is larger and more irregular in 

 outline than the neighboring small tributaries of the vein. ]^o 



tr ep 



Fig. 4. From a human embryo of 22.8 mm. (H. E. C, 871). x 20 diam. 

 The ribs, clavicle, scapula, and humerus have been stippled, and the sub- 

 clavius muscle has been drawn. In addition to the veins shown in Fig. 1, the 

 following are included: T. an. dext., Vena anonyma dextra; V. an. sin., V. 

 auonyma sinistra ; V. hr., V. brachialis ; F. cepJi., V. cephalica ; V. jug. ant., 

 V. jug. ext., V. jtig. int., Y. jugularis anterior, externa, interna ; V. mam. int., 

 v. mammaria interna. 



lymphatics could be found in a 9.2 mm. embryo, so that the jugular 

 lymphatics probably arise in human embryos of about 10 mm. This 

 accords with the observation that they first appear in rabbits of 

 9.5-10.0 mm., but does not agree with Ingalls' opinion that in a 

 4.9 mm. human embryo certain vessels represent "the first anlage, or 



