OLFACTORY NERVES. 



659 



membrane, extends from the cribiform plate of the ethmoid bone downward 

 a little less than an inch (25 mm.). It is soft and friable, very vascular, 

 thicker than the rest of the Schneiderian membrane, and in man, it has rather 

 a yellowish color. It is covered by long, delicate, columnar cells, nucleated, 

 and each one provided with three to eight ciliary processes, the movements of 

 which are from before backward. The olfactory membrane is provided with 

 a large number of long, racemose, mucous glands, which secrete a fluid that 

 keeps the surface moist, a condition essential to the accurate perception of 

 odorous impressions. 



OLFACTORY (FIRST NERVE). 



The apparent origin of the olfactory nerve is by three roots, from the 

 inferior and internal portion of the frontal lobe of the cerebrum, in front of 

 the anterior perforated 

 space. The three roots 

 are an external and an 

 internal white root, and 

 a middle root composed 

 of gray matter. The 

 external white root is 

 long and delicate, pass- 

 ing outward, across the 

 fissure of Sylvius, to 

 the temporo-sphenoidal 

 lobe. The internal white 

 root is thicker and short- 

 er than the external root, 

 and it arises from the 

 most posterior portion 

 of the frontal lobe. The 

 middle, or gray root 

 arises from a little em- 

 inence of gray matter 

 situated on the posterior and inner portion of the inferior surface of the 

 frontal lobe. 



The deep origin of these three roots of the olfactory nerves is still a matter 

 of discussion. The external root passes through the gray substance of the 

 island of Reil, to a gray nucleus in the temporo-sphenoidal lobe, in front of 

 the pes hippocampi. The fibres of the middle root have not been traced 

 farther than the gray eminence from which it arises. The fibres of the inter- 

 nal root probably are connected with the fibres of the gyrus fornicatus. The 

 three roots converge to form a single cord at the inner boundary of the fissure 

 of Sylvius. This cord passes forward and slightly inward, in a deep groove be- 

 tween two convolutions on the under surface of the frontal lobe, covered by 

 the arachnoid membrane, to the ethmoid bone. This portion of the nerve is 

 soft and friable. It is composed of both white and gray matter, the propor- 



Fro. 235. Olfactory ganglion and nerves (Hirschfeld). 

 1, olfactory ganglion and nerves ; 2, branch of the nasal nerve ; 3, 

 spheno-palat'ine ganglion ; 4, 7, branches of the great palatine 

 nerve ; 5, posterior palatine nerve ; 6, middle palatine nerve ; 8, 9, 

 branches from the spheno-palatine ganglion ; 10, 11, 12, Vidian 

 nerve and its branches ; 13, external carotid branch, from the su- 

 perior cervical ganglion. 



