THE PIGEON. 257 



part of the brain not separated off from the medulla oblongata, 

 but answering to the crura cerebri. 



347. The fourth nerve (iv), arising from the dorsal 

 side of the medulla oblongata at its anterior end : it emerges 

 between the medulla and the cerebellum, and passes down- 

 wards in the groove between the medulla and the optic lobe 

 to reach the ventral surface of the brain. 



348. The fifth nerve (v), a large trunk arising from the 

 lateral surface of the medulla oblongata just behind the 

 optic lobe : its fibres extend upwards quite to the dorsal 

 edge of the medulla. 



The fifth nerve arises by two roots, the larger of which presents an 

 enlargement, the Gasserian ganglion. 



349. The sixth nerve (vi), arising from the ventral 

 surface of the medulla near the middle line and just internal 

 to the point of origin of the fifth. 



350. The seventh nerve (vii), a small trunk arising 

 close behind the fifth. 



351. The eighth or auditory nerve (viii), a large, soft 

 trunk arising close behind the seventh : its fibres are traceable 

 upwards to the dorsal pyramids of the medulla. 



352. The ninth (ix), tenth (x), and eleventh (xi) 

 nerves, arising together close behind the eighth : they 

 have small roots, the tenth (vagus) being the largest, and 

 the eleventh (spinal accessory) distinguished by being 

 traceable upwards and backwards alongside the medulla 

 oblongata to the spinal cord, from which it arises between 

 the roots of the spinal nerves, also receiving fibres from the 

 medulla. 



353. The tvs^elfth nerve or hypoglossal (xii), a 

 small trunk arising from the ventral surface of the medulla 

 internal to the eleventh. 



