THE ECTODERM AND ITS DERIVATIVES 



187 



Noto- White Neural Gray Dorsal Ramus 



chord matter canal matter root communicans 



Ventral 

 root 





Noto- Sympa- Dorsal Ramus Muscle Muscle Noto- Caudal Neural Nerve 

 chord thetic aorta commu- chord artery canal cord 



ganglion nicans 



Development of the spinal cord and sympathetic nerves. (A) Showing the 

 dorsal root (from neural crest). (B) Showing the ventral root (from cord 

 neuroblasts). (C) Showing connection between the spinal nerve and the sympa- 

 thetic ganglion, known as the ramus communicans. (D) A section in the tail 

 region to show the relatively large notochord and reduced nerve cord. 



