CEREBKO-SPINAL NERVES 391 



CEKEBEO-SPINAL NERVES 

 THE CRANIAL OR ENCEPHALIC NERVES 



If we examine the base of the brain, a number of nerves are seen to 

 come off from its surface. They vary in size, as they do also in function, 

 and among them are numbered the nerves of the special senses of smell, 

 sight, taste, and hearing. The cranial nerves are arranged symmetrically on 

 either side of the base of the brain, and for the most part distribute their 

 branches to parts on the side from which they arise. There is a want of 

 agreement in this country between human and veterinary anatomists as 

 to the enumeration of the cranial nerves. By the one they are described 

 as nine, by the other as twelve. We need not, however, enter into the 

 pros and cons of this question here, but we give below the numerical 

 designations of each: 



Name. Veterinary. Human. 



Olfactory Nerves ... 1 1 



Optic Nerves 2 2 



Oculomotor Nerves ... ... ... 3 



Pathetic Nerves 4 



Trifacial or Lingual Nerves 5 5 



Abducent Nerves ... ... ... 6 6 



Facial Nerves (Portio dura) 7 j ^ 



Auditory Nerves (Portio mollis) ... 8/ 



Glosso-pharyngeal Nerves 9^ 



Pneumogastric or Vagus Nerves 10J- 



Spinal Accessory Nerves ... 

 Hypoglossal Nerves 



First Pair, Olfactory. The first pair of cranial nerves is the olfac- 

 tory, a number of fine filaments whose superficial origin is the olfactory 

 bulbs. These bulbous bodies are lodged in the ethmoidal fossae of the 

 ethmoid bone, two depressions in front of the cranium, in which a number 

 of minute openings appear and allow of their passage out of the cranium 

 into the superior parts of the nostrils, where they are distributed over the 

 schneiderian membrane. 



The olfactory nerves are the first pair of special nerves, whose function 

 is that of receiving the impressions of odours, which they carry 



brain. 



Second Pair, Optic Nerves.-These nerves are derived from two 

 thick bands which wind round the crura cerebri in their co 

 their deep origin in the corpora quadrigemina. 



On reaching the inferior surface of the cranium, the two optic bands 



