CRANIAL SYMPATHETIC GANGLIA IN THE RAT 



185 



An examination of later stages — sixteen- and seventeen-day 

 embryos — affords some few additional facts. The ganglionic 

 mass at the origin of the recurrent nerve has increased somewhat 

 in size. Ganglia on the branches of the inferior laryngeal nerve 

 and on small vagus branches below the exit of this nerve have 

 assumed a constant position as regards the trachea and esophagus. 

 They are situated between the trachea and the esophagus ; their 

 number is not constant, averaging perhaps eight per side; as 



S.N. X 



Fig. 6 Rat embryo. 15f days, vom Rath's technique. Neuroblasts along; 

 duodenal branches of vagus. Projection drawing, X 500. 



one might assume from their origin, they are bilaterally sym- 

 metrical. The ganglia tend to be irregular in shape, rather 

 diffuse groups of cells shading into one another; occasionally 

 they are well formed, compact masses. They possess transverse, 

 intercommunicating strands and give off branches to the develop- 

 ing musculature of the trachea. Apparently the occasional 

 neuroblasts which may now be encountered in the developing 

 muscularis of the esophagus and were not found in earlier stages 

 owe their origin to cells found in vagus and inferior laryngeal 

 strands independent of these so-called tracheo-esophageal gan- 



