32 THE FROG 



is thin and covered by the posterior chorioid plexus 



which usually comes off with the overlying bone, 

 to expose the fourth ventricle (201). 



180. The spinal cord should be traced back as far as 

 the first spinal nerve (152). 



The cranial nerves of the frog are small and the dissection 

 of them is difficult. Identify the following nerves from the 

 dorsal aspect. 



181. The olfactory nerve (I) arises from the olfactory 

 lobe and runs to the nose. 



182. The trochlear nerve (IV), very small, arises from 

 the brain between the optic lobes and the cerebellum. 

 (It supplies one of the eye muscles.) 



183. The trigeminal nerve (V) arises from the medulla 

 at its cephalo-lateral angle and passes into the 

 prootic ganglion, where it is joined by 



184. the facial nerve (VII). 



From the prootic ganglion trace forward five branches. 



185. The caudal branch is the hyomandibular ramus of 

 the Vllth. 



186. Anterior to this the maxillo-mandibular ramus of 

 the Vth arises. 



187. Next the temporal ramus of the Vth is given off. 



188. Ventral to these is the ophthalmic ramus of the Vth. 



189. Ventral to the hyomandibular ramus, the palatine 

 ramus of the Vllth takes its origin. 



190. The auditory nerve (VIII) leaves the brain close 

 behind the Vllth and passes directly to the ear. 



191. The glossopharyngeal nerve (IX) arises from the 

 sides of the medulla by four roots which it possesses 

 in common with the tenth cranial nerve, with which 

 it is associated. 



