ANTERIOR CRANIAL NERVES OF PIPA AMERICANA. 127 



VIII(Auditory)VII(Facial) and V(Trigeminal) nerves. 

 These three nerves have a common origin from the side 

 of the medulla oblongata, arising by fibres among which 

 the roots of separate nerves cannot be distinguished. 



The auditory nerve separates directly and goes to the 

 large auditory ganglion, situated in a foramen in the wall 

 of the otic capsule immediately opposite the common ori- 

 gin of the three nerves from the medulla. 



From this ganglion three groups of nerves arise, which 

 may be taken up in order, beginning with the most poste- 

 rior. The posterior ramus or group consists of the ram- 

 ulus posterior (r.p.), the ramulus neglectus (r.a.neg.), 

 the ramulus basilaris (r.bas.), and the ramulus lagense 

 (r.a.lag.). The ramulus posterior leaves the posterior 

 side of the ganglion, and runs outward and backward to 

 the ampulla of the posterior semicircular canal, over the 

 sensory epithelium of which it is distributed. The ramu- 

 lus neglectus leaves the ganglion in company with the pre- 

 ceding nerve and soon distributes itself to the pars neglecta 

 of the sacculus. The ramulus basilaris has a similar 

 course to the pars basilaris of the cochlea. The fourth 

 and last of this group, the ramulus lageuae, has a more 

 ventral origin and runs somewhat ventrally to the lagena. 

 The second branch of the Auditory nerve, the ramulus sac- 

 culi, consists of a large branch running outward and 

 spreading slightly, forming a large brush distributed over 

 the macula acustica on the lower side of the sacculus. 

 The third group consists of the nerves to the two anterior 

 ampullae. They arise as a single nerve from the anterior 

 side of the ganglion and run forward and outward. Then 

 they divide to go to their respective ampullae. The ram- 

 ulus anterior (r.a.a.) makes a turn around the external 

 semicircular canal to reach its own ampullae. 



After the separation of the auditory nerve, the V and 



ESSEX INST. BULLETIN, VOL. XXV 18 



