LSI ALBERT Kl'NTZ 



ciirW. Nevertheless, the writer is still of the opinion that the 

 (^ai'liest cells enter the primordia of the sympathetic trunks in 

 achance of the ^rowin^' fibers. 



'i'liat a Hhious tract is not essential foi* the peripheral migration 

 of cells of cerel)i()spinal origin is obvious in embr^^os of the turtle 

 in which, as observed by the writer in an earlier paper Cll), 

 many of the cells which enter the primordia of the sympathetic 

 trunks advance fiom the spinal nerves, not along the paths of 

 the commimicating rami, but directly through the mesenchyme. 

 This observation was corroborated by Ganhni ('14) in embryos 

 of other reptilian types. Obviously, if cells entering the sympa- 

 thetic primordia could not be displaced in advance of the growing 

 nerve fibers or in the absence of a fibrous path, the cells consti- 

 tuting the primordia of the sympathetic trunks would not occur 

 as widely scattered in the mesenchyme as is the case even in 

 human embryos. 



The peripheral migration of cells of cerebrospinal origin into 

 the primordia of the sympathetic trunks continues actively in 

 human embryos for some time after the communicating rami 

 have become fibrous. During the same interval the number of 

 cells in these primordia is materially increased by local cell 

 division. Human embryos 10 mm. and over in length afford 

 little evidence that migration of cells along the communicating 

 rami continues after a length of 12 mm. has been attained. 



Relatively few careful observations on the development of the 

 cervical portions of the sympathetic trunks have been recorded. 

 All who made special mention of these structures in embryos ol 

 the higher vertebrates noted that their primordia arise later 

 than the piimoidia of the thoracic portions of the sympathetic 

 trunks. They also noted that there occurs a gradual extension 

 of the cell-columns which constitute the primordia of the sympa- 

 thetic trunks from the upper thoracic region cephalad until the 

 level of the first cervical nerve is reached. Nevertheless, the 

 general impression that each pair of cervical spinal nerves makes 

 its contribution of cells to these primordia seems to prevail. 

 Cianfini ('17) maintains that in early embryos both of the 

 guinea-pig and the pig cellular communicating rami extend from 



