92 HUMAN PHYSIOLOGY. 



ist Pair. Olfactory. 



Apparent Origin. From the inferior and internal portion of the ante- 

 rior lobes of the cerebrum by three roots, viz. : an external white root, 

 which passes across the fissure of Sylvius to the middle lobe of the cere- 

 brum ; an internal white root, from the most posterior part of the anterior 

 lobe ; a gray root, from the gray matter in the posterior and inner portion 

 of the inferior surface of the anterior lobe. 



Deep Origin. Not satisfactorily determined. 



Distribution. The olfactory nerve, formed by the union of the three 

 roots, passes forward along the under surface of the anterior lobe to the 

 ethmoid bone, where it expands into the olfactory bulb. This bulb con- 

 tains ganglionic cells, is grayish in color and soft in consistence ; it gives 

 off from its under surface from fifteen to twenty nerve filaments, the true 

 olfactory nerves, which pass through the cribriform plate of the ethmoid 

 bone, and are distributed to the schneiderian mucous membrane. This 

 membrane extends from the cribriform plate of the ethmoid bone down- 

 ward, about one inch. 



Properties. The olfactory nerves give rise to neither motor nor sensory 

 phenomena when stimulated. They carry simply the special impressions 

 of odorous substances. Destruction or injury of the olfactory bulbs is 

 attended by a loss of the sense of smell. 



Function. Governs the sense of smell. Conducts the impressions 

 which give rise to odorous sensations. 



2d Pair. Optic. 



Apparent Origin. From the anterior portion of the optic commissure. 



Deep Origin. The origins and connections of the optic tract are very 

 complex. The immediate origins are bands of fibres from the thalamus 

 opticus and anterior corpora quadrigemina. The corpora geniculata are 

 interposed ganglia. The ultimate roots are traced 



1. By abroad band of fibres "the optic radiation of Gratiolet " to 



the psycho-optic centres in the occipital lobes. 



2. To the gyrus hippocampi and sphenoidal lobes. 



3. Through the corpus callosum to the motor areas of the opposite cere- 



bral hemispheres. 



4. To the frontal region by " Meynert's Commissure." 



5. To the spinal cord. 



6. To the corpora geniculata, pulvinar, and anterior corpora geniculata 



by ganglionic roots. 



