420 NERVES OF ENCEPHALON. 



cvale minus. The other hemisphere, cut in the same way, 

 presents a similar view ; and the two together receive the 

 name of centrum ovale majus, which is nothing more than 

 the white central mass of medullary matter, surrounded 

 by gray or cineritious substance. (Fig. 11*7.) 



NERVES OF THE ENCEPHALON. (Fig. 16.) 



The nerves of the encephalon are nine pair, according to 

 the old nomenclature, and eleven or twelve pair according 

 to the more modern. The additional number is arrived at 

 by making two out of the seventh and three out of the 

 eighth pair. 



M. Cruveilhier remarks it is more philosophical to exam- 

 ine the nerves of the brain from behind forward, but as it is 

 more convenient in the removal of the brain, to study these 

 nerves then, we shall adopt the usual plan, and describe 

 them from before backward, and in their numerical order. 



First Pair, or Olfactory Nerves, (Fig. 118.) These are the 

 nerves of smell, and are situated on the lower surface of 

 the anterior lobes of the cerebrum. Each arises by three 

 filaments, one of which is external from the fissure of Syl- 

 vius, long and white ; the second internal from the corpus 

 callosum, and the middle, gray, from the posterior convolu- 

 tion of the anterior lobe. The three unite to form a soft, 

 gray, triangular nerve, having a bulbous expansion, which 

 is lodged between the convolutions, where it is protected 

 and covered by the arachnoid membrane. Each bulb rests 

 on the cribriform plate of the ethmoid bone, on either side of 

 the crista-galli, whence proceed numerous filaments through 

 the various foramina in this plate to the mucous membrane 

 of the nose. These divide into two sets, an internal, and 

 an external, the former going to the septum, the latter to the 

 upper and middle spongy bones. These nerves differ from 

 all others in their shape, which is triangular, and in their 

 structure, which is very soft, some fibres being white, others 

 gray, and in not being surrounded by the arachnoid. Their 

 bulbs are called by Mr. Solly the olfactory ganglia. 



Second Pair, or Optic. These are the nerves of sight. 



