SYMPATHETIC NERVOUS SYSTEM IN MAN 185 



the cervical spinal nerves toward the primordia of the sympa- 

 thetic trunks and that ' neurocytes ' advance into the latter along 

 these cellular rami. These cellular rami disappear early, accord- 

 ing to Ganfini, after which there are no connections between the 

 cervical spinal nerves, except the last, and the sympathetic 

 trunks until the fibers which constitute the gray communicating 

 rami are present. Although the writer has given especial atten- 

 tion to the development of the cervical portion of the sympathetic 

 trunks, both in human embryos and in embryos of the pig, he 

 was unable to substantiate this observation of Ganfini, nor could 

 he obtain any evidence that the cervical spinal nerves with which 

 no white communicating rami are associated play any part in 

 the development of the sympathetic trunks. The wTiter's obser- 

 vations indicate that the primordia of the sympathetic trunks 

 grow cephalad from the lower cervical region both by the dis- 

 placement of cells along the dorsal aspect of the descending aortae 

 and by local cell division. In this connection Streeter's obser- 

 vation that in the cervical and upper thoracic regions the pri- 

 mordia of the sympathetic trunks are not segmental, but "the 

 cells remain massed in larger clumps, and these result in ganglia 

 corresponding to from two to five segments," is not without 

 interest. The cervical portions of the primordia of the sympa- 

 thetic trunks are indeed continuous cell-columns until the con- 

 densations which result in the ganglia characteristic of the 

 cervical sympathetic trunks are initiated. 



In embryos 10 mm. in length the cell-masses constituting the 

 primordia of the sympathetic trunks have become larger and more 

 compact (fig. 16, sy). Although some of the cells still remain 

 somewhat scattered, the segmental character of the sympathetic 

 trunks is becoming more apparent and longitudinal fibers are 

 present; however, the rami connecting the adjacent ganglia are 

 nowhere free from sympathetic cells. As development advances 

 the curvature of the embryo becomes less marked, and the ganglia 

 of the sympathetic trunks become more widely separated. These 

 ganglia also become more compact and more sharply delimited. 

 In sagittal sections of an embryo 15 mm. in length (no. 390) the 

 segmental character of the sympathetic trunks is well marked 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 32, NO. 2 



