222 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



represent part of a posterior root ganglion. From these ganglia 

 are developed the sensory visceral fibres connected with the fore 

 gut and all the structures derived from the fore gut or splanchno- 

 pleure of the fore gut. A vestigial posterior root ganglion may 

 occur on the 12th nerve. 



The circuitous course of the spinal accessory is probably due to 

 the migration of the trapezius caudalwards from a cephalic to its 

 present position. 



