SYMPATHETIC TRUNKS IN CHICK 



341 



Number 3. In this embryo the operation involved the ner- 

 vous system in the lower thoracic and lumbar regions. The neural 

 tube is reduced to less than one third its normal size in not less 

 than ten successive segments. Spinal ganglia and dorsal nerve- 



Fig, L Transverse section from a segment of embryo number 1, in which 

 spinal ganglion and dorsal nerve-root are absent. X 165. AO, aorta; CR, 

 communicating ramus; DR, dorsal ramus; A', notochord; SY, sympathetic 

 trunk; VR, ventral root of spinal nerve. 



A. Camera lucida outline of a cross section of the remnant of the neural tube 

 (X) in the segment from which figure 1 is taken superimposed on a camera lucida 

 outline of the same magnification of a cross section of the neural tube (Y) a few 

 segments farther cephalad where it was not affected by the operation. 



