THE LIZARD. 179 



in the middle line of the ventral surface of the brain, imme- 

 diately under the pineal body, and attached to an elevation, 

 the infundibulum. 



230. The thalamencephalon, seen by slightly separat- 

 ing the posterior ends of the cerebral hemispheres as a 

 rounded median mass, interposed between the hemispheres 

 and the optic lobes : the infundibulum is a ventral, back- 

 wardly-directed prolongation of the thalamencephalon. 



231. The optic chiasma (o.c), an x-shaped body situated 

 immediately anterior to the infundibulum, and consisting 

 of the optic tracts (o.t), which pass backwards and slightly 

 upwards on either side of the infundibulum to the anterior 

 ventral region of the optic lobes, and of the optic (second) 

 nerves (II), which, becoming free from the brain, pass 

 forwards and outwards to the eyes. 



232. The third nerve (III), arising from the ventral surface of the 

 mid-brain. 



233. The fourth nerve (IV), arising from the dorsal surface of the 

 medulla oblongata, just in front of the cerebellum. 



234. The fifth nerve, or trigeminal (V), arising from the ventro- 

 lateral region of the medulla. 



235. The sixth nerve (VI), a small nerve arising from the ventral 

 region of the medulla, not far from the middle line. 



236. The seventh nerve (VII), arising in common with the eighth 

 from the lateral surface of the medulla, just posterior to the fifth. 



237. The eighth, or auditory nerve (VIII), arising in common 

 with the seventh. 



238. The ninth nerve, or glossopharyngeal (IX), arising imme- 

 diately behind the eighth, and at a somewhat lower level. 



239. The tenth nerve, or vagus (X), arising just posterior to the 

 ninth, by three or four separate roots. 



240. The eleventh nerve, or spinal accessory (XI), arising from 

 the spinal cord, and passing forwards, receiving fibres as it goes, to the 

 medulla oblongata, which it finally leaves immediately behind the 



vagus. 



241. The twelfth nerve, or hypoglossal (XII), arising a little 

 behind the eleventh from the ventral surface of the medulla. 



N 2 



