THE OLFACTORY NERVES 



881 



THE CRANIAL NERVES (NERVI CEREBRALES; CEREBRAL NERVES). 



There are twelve pairs of cranial nerves; they are attached to the brain and 

 are transmitted through foramina in the base of the cranium. The different pairs 

 are named from before backward as follows: 



I 1st. Olfactory. 7th. 



2d. Optic. 8th. 



3d. Oculomotor. 9th. 



4th. Trochlear. 10th. 



5th. Trigeminal. llth. 



6th. Abducent. 12th. 



Facial. 



Acoustic. 



Glossopharyngeal . 



Vagus. 



Accessory. 



Hypoglossal. 



The area of attachment of a cranial nerve to the surface of the brain is termed 

 its superficial or apparent origin. The fibers of the nerve can be traced into the sub- 

 stance of the brain to a special nucleus of gray substance. The motor or efferent 

 cranial nerves arise within the brain from groups of nerve cells which constitute 

 their nuclei of origin. The sensory or afferent cranial nerves arise from groups 

 of nerve cells outside the brain; these nerve cells may be grouped to form ganglia 

 on the trunks of the nerves or may be situated in peripheral sensory organs such 

 as the nose and eye. The central processes of these cells run into the brain, and 

 there end by arborizing around nerve cells, which are grouped to form nuclei of 

 termination. The nuclei of origin of the motor nerves and the nuclei of termination 

 of the sensory nerves are brought into relationship with the cerebral cortex, the 

 former through the geniculate fibers of the internal capsule, the latter through 

 ;he lemniscus. The geniculate fibers arise from the cells of the motor area of the 

 cortex, and, after crossing the middle line, end by arborizing around the cells of the 

 nuclei of origin of the motor cranial nerves. On the other hand, fibers arise from 

 che cells of the nuclei of termination of the sensory nerves, and after crossing to 

 the opposite side, join the lemniscus, and thus connect these nuclei, directly or 

 indirectly, with the cerebral cortex. 



THE OLFACTORY NERVES (NN. OLFACTORH; FIRST NERVE) (Fig. 771). 



The olfactory nerves or nerves of smell are distributed to the mucous membrane 

 of the olfactory region of the nasal cavity : this region comprises the superior nasal 



Fibers of olfactory 

 tract 



Mitral cells 



Glomeruli 



Olfactory cell 



Olfactory 

 epithelium 



FIG. 771. Nerves of septum of nose. Right side. 



FIQ. 772. Plan of olfactory neurons. 



concha, and the corresponding part of the nasal septum. The nerves originate 

 from the central or deep processes of the olfactory cells of the nasal mucous mem- 





