NEUROLOGY 265 



Certain non-medullated axones are surrounded by a delicate, 

 homogeneous, nucleated sheath, called the neurilemma, or sheath of 

 Schwann. 



THE CRANIAL NERVES 



The cranial nerves have their origin in the brain and leave the 

 cranial cavity in pairs. They are numbered numerically from before 

 backward, there being twelve pairs in all. The following is a tabu- 

 lation according to their number, name, and function: 



No. Name Pimctional Nature 



I. Olfactory Smell-sense 



II. Optic Visual-sense 



III. Oculomotor Motor to muscles of eyeball and orbit 



rV. Pathetici Motor to superior oblique muscle of eyeball 



V. Trifacial Mixed: Sensor to face and tongue. Motor to face 



VI. Abducentes Motor to External rectus of eyeball 



Vn. Facial Motor to muscles of head and face 



VIII. Auditory Hearing-sense 



DC. Glossopharyngeal Mixed: Tongue, pharynx and muscles of throat 



X. Vagus Mixed: Sensori-motor to respiratory tract and part 



of alimentary tract 



XI. Spinal accessory Motor to muscles of pharynx, neck and heart 



XII. Hypoglossal Motor to muscles of the tongue 



Olfactorius. — Nervus olfactorius (Fig. 75, C, 16). This is the 

 nerve of smell, one of the nerves of special sense. The organ of 

 smell consists of five layers as follows: 



First, a layer of olfactory fibers extending in dififerent directions 

 and consisting of a dense plexiform arrangement of the axones of 

 the olfactory cells. From this layer the fibers pass into the layer 

 of olfactory glomeruli where their terminal ramifications mingle 

 with the dendritic terminals of cells lying in the more dorsal layers, 

 to form distinctly outlined spheroidal or oval nerve fiber nests, the 

 olfactory glomeruli. 



Second, a. fine granular layer of basic substance containing round 

 cellular structures, the stratum granulosum. 



Third, broader granular, or molecular layer, having on its inner 

 surface a row of large pjoramidal cells which are both small and large 

 and which send their dendrites into the olfactory glomeruh. Their 

 points are directed outward. 



Fourth, a layer of round cells tightly pressed together and measur- 

 ing about 5 microns in diameter. Between these cells are very 

 fine nerve fibers. 



