MEDULLA OBLONGATA OF THE RABBIT. 



19 



to me that there can be no doubt that in the embryonic 

 rabbit the tractus solitarius is formed by nerve fibres 

 derived from the posterior nerve roots of the V (VII and 

 VIII), IX, and X ganglia. 



Fig. 14. 



Section of the medulla of an embryo rabbit 14 mm. at right angles to the floor 

 of the fourth ventricle in the region of the VII and VIII ganglia. F, ganglion 

 vestibuli. (r, ganglion geniculi. C, ganglion cochleae. TS^ tractus solitarius. 

 02^, otic vesicle. Int C, internal carotid. J", jugular vein. 



Thus the tractus solitarius is rendered a much more 

 important structure than has been previously assumed, since 

 more nerve fibres enter into its formation. This fact, more- 

 over, demonstrates the great similarity which exists between 

 the four great cranial ganglia — the V (VII, VIII), IX, 

 and X — a fact which hitherto has only been held as a 

 supposition. 



