Johnston, Nerves of Petromyzonts. 



589 



above are fibers of the VII nerve. In Fig. 19 ^ is show^n the 

 interlacing of the fibers of the two nerves as it appears in a section 

 directly dorsal to the gill opening. Fibers going forward from the 

 IX nerve supply also the thin sheet of muscle covering the posterior 

 wall of the first gill sac. 



Fig. 19. A horizontal section through the external opening (ex.o.) of the first gill sac on the left 

 side, showing the branches of the VII and IX nerves related to it. h.v., blood vessel. At A is shown 

 a section passing just dorsal to the same gill opening to show the intermingling of the VII and IX fibers 

 in the epithelium. Magnification, 60 diameters. 



