288 ALBERT KUNTZ 



rami (fig. 2, C, s. sy.). These ganglionic enlargements are at 

 first independent of each other, but become united later by longi- 

 tudinal commissures. Like the anlagen of the primary sympa- 

 thetic trunks, the anlagen of the secondary sympathetic trunks 

 appear earliest in the thoracic region and latest in the sacral 

 region. At the beginning of the sixth day there are as yet 

 no traces of the anlagen of the secondary sympathetic trunks 

 in the posterior half of the body. During the course of the sixth 

 day, the secondary sympathetic trunks become larger and 

 more conspicuous, while the primary sympathetic trunks become 

 correspondingly smaller. The former, being located at the point 

 of origin of the communicating rami, are connected with the latter 

 by the cellular tracts which connect them with the spinal nerves 

 (fig. 2, C). 



As the communicating rami become fibrous, the anlagen of the 

 secondary sympathetic trunks become removed a short distance 

 from the spinal nerves. In the cervical and the thoracic region 

 they are removed to the ends of the short communicating rami 

 (fig. 2, D, s. sy.). In the posterior region of the body, the fibers of 

 the communicating rami extend beyond the anlagen of the secon- 

 dary sympathetic trunks. At the close of the sixth day, they may 

 be traced through the cell-aggregates still remaining scattered 

 along the sides of the aorta, into the anlagen of the prevertebral 

 plexuses. 



In the posterior region of the body, the distinction between the 

 primary and the secondary sympathetic trunks is never well 

 marked. Cells gradually become aggregated in the proximal part 

 of the communicating rami to give rise to the secondary sympa- 

 thetic trunks, while the cells constituting the primary sympathetic 

 trunks migrate ventrally into the anlagen of the prevertebral 

 plexuses. After the sixth day, the secondary sympathetic trunks 

 become more distinct throughout their entire length, as the gan- 

 glionic enlargements become connected by the fibers of the longi- 

 tudinal commissures. 



(d.) Histogenesis. — As already indicated, the sympathetic trunks 

 arise from cells which migrate peripherally from the cerebro- 

 spinal nervous system along the spinal nerves. As soon as fibers 



