SYMPATHETIC SYSTEM IN TURTLES 293 



The breaking up of the anlagen of the sympathetic trunks, the 

 formation of secondary cellular tracts extending from the proxi- 

 mal parts of the spinal nerves into the sympathetic anlagen, and 

 the proximal shifting of the origin of the communicating rami 

 along the spinal nerve-trunks above described, which are so con- 

 spicuous in embryos of the turtle, in all probability, represent a 

 condition which is characteristic of reptiles and which has phylo- 

 genetic significance. 



His, Jr., ('97) called attention to the fact that in the chick two 

 pairs of sympathetic trunks arise in the course of ontogeny. These 

 he has designated as the 'primary' and the 'secondary' sym- 

 pathetic trunks. In my work on the development of the sympa- 

 thetic nervous system in birds,^ I was able to substantiate this 

 observation of His, Jr. The primary sympathetic trunks in the 

 chick arise about the beginning of the fourth day of incubation, 

 as a pair of cell-columns lying along the sides of the aorta and along 

 the dorsal surfaces of the carotid arteries. The anlagen of the 

 secondary sympathetic trunks arise about the beginning of the 

 sixth day of incubation, as ganglionic enlargements on the median 

 sides of the spinal nerves. The cells giving rise to both the pri- 

 mary and the secondary sympathetic trunks migrate peripher- 

 ally from the spinal ganglia and from the ventral part of the neural 

 tube along the paths of the spinal nerves. In the early stages some 

 of the cells advancing peripherally along the paths of the spinal 

 nerves deviate from the course of the latter and wander toward the 

 lateral surfaces of the aorta where they become aggregated to give 

 rise to the primary sympathetic trunks. A little later the cells 

 advancing peripherally no longer wander toward the aorta, but 

 become aggregated at the median sides of the spinal nerves to 

 give rise to the anlagen of the secondary sympathetic trunks. 

 As development advances and the communicating rami grow 

 mesially the entire cell-aggregates constituting the anlagen of the 

 secondary sympathetic trunks are displaced toward the aorta at 

 the distal ends of the growing communicating rami. As the second- 



' The development of the sympathetic nervous system in birds. Jour. Comp. 

 Neur. Psych., vol. 20, no. 4, pp. 283-308. 



