THE OLFACTORY KERVE. 527 



Distribution. — The olfactory nerve is exclusively distributed to the 

 nasal fossae. 



From the under surface of the olfactory bulb about twenty branches 

 proceed throug-h the holes in the cribriform plate of the ethmoid bone, 

 each invested by tubular prolongations of the membranes of the brain. 

 These tubes of membrane vary in the extent to which they are con- 

 tinued on the branches : the offsets of the dura mater sheathe the 

 filaments, and join the periosteum linmg the nose ; those of the pia 

 mater and arachnoid become blended with the neurilemma of the 

 nerves. 



Fig. 332. 



Fig. 332. Distribution op the Olfactory Nerves on the Septum op the Nose 

 (from Sappey after HirschfelJ and Leveille). § 



The septum is exposed and tbe anterior palatine canal opened on the right side. I, 

 placed above, points to the olfactory bulb, and the remaining Roman numbers to the 

 roots of the several cranial nerves ; 1, the small olfactory nerves as they pass through the 

 cribriform plate ; 2, internal or septal twig of the nasal branch of the ophthalmic nerve ; 

 3, naso-palatine nerves. (See fig. 339 for a view of the distribution of the olfactory 

 nerves on the outer wall of the nasal fossa. ) 



The branches are aiTanged in three sets. Those of the inner set, 

 lodged for some distance m grooves on the surface of the bone, ramify 

 in the pituitary membrane of the septum ; the outer set extend to the 

 upper two spongy bones and the smooth surface of the ethmoid bone in 

 front of these ; and the middle set, which are very short, are confined 

 to the roof of the nose. The distribution of the olfactory nerve is con- 

 fined to the upper part of the nasal fossa ; none of the branches reach 

 the lower spongy bone. — (See Anatomy of the Nose.) 



OPTIC NERVE. 



The second pair or optic nerves of the two sides meet each other at 

 the optic commissure (chiasma), where they partially decussate. From 

 this point they may be traced backwards round the crura cerebri, under 

 the name of the optic tracts. 



Surface attachment. — Each optic tract arises from the posterior 

 part of the optic thalamus and the corpora geniculata. As it leaves 

 the under part of the thalamus, it makes a sudden bend forwards and 

 then runs obliquely across the under surface of the cerebral peduncle. 



