ZOOTOMY. 



arising from the external edges of the anterior pyramids of 

 the medulla, just posterior to the pons. 



492. The facial nerves, or portiones durse (seventh 

 pair, VI I \ arise from the lateral regions of the ventral 

 surface of the medulla, just posterior to the corresponding 

 nerves of the fifth pair; their fibres pass directly outwards. 



493. The auditory nerves, or portiones molles 

 (eighth pair, VIII), arise close behind and slightly external 

 to the facials ; each divides immediately into two large 

 trunks, which pass outwards, parallel with the corresponding 

 seventh nerve. 



494. The glossopharyngeal nerves (ninth pair, IX), 

 vagi or pneumogastric nerves (tenth pair, X), and 

 accessory nerves (eleventh pair, XI), arise, in the order 

 mentioned, from the lateral regions of the medulla, just 

 posterior to the cerebellum, and so close to one another that 

 they may easily be mistaken for a single pair. If a sufficient 

 length of the spinal cord has been removed along with the 

 brain, the accessory will be seen to be formed by a slender 

 nerve which arises from the spinal cord slightly posterior to 

 the fifth spinal nerve, and passes forwards, receiving fibres 

 from the cord as it goes, between the dorsal and ventral 

 roots of the first five spinal nerves. 



495. The hypoglossal nerves (twelfth pair, XII) 

 arise from the external edges of the anterior pyramids of 

 the medulla, slightly posterior to the three preceding nerves ; 

 each is formed by the union of several strands, which closely 

 resemble those of the ventral root of a spinal nerve. 



LVIL Place the brain with its dorsal side upwards, 

 and carefully remove successive slices from one of 

 the hemispheres parallel to its upper surface, until 

 the upper surface of the corpus callosum is reached 

 (be careful not to go beyond this point, or some 



