THE ENCEPHALIC OR CRANIAL NERVES 625 



comes swollen, vascular, and liable to hemorrhage on the slightest irritation. 

 The degenerative changes may lead to a complete loss of smell. These results 

 were formerly attributed to a loss of trophic influence which it was believed 

 the nerve exercised over these structures. Modern experimentation and 

 various surgical procedures have demonstrated that the nutritive disorders 

 -,are septic in origin, made possible by the anesthetic condition and by the 

 changed vascular supply from division of the vasomotor fibers which join the 

 nerve at or near the ganglion. 



Origin of the Efferent Axons. The efferent axons arise for the 

 most part from nerve-cells located in the- gray matter beneath the upper 

 half of the floor of the fourth ventricle. A group of cells known as the 

 superior or accessory nucleus, situated posterior to the corpora quadngem- 

 ina, gives origin to axons which descend and join the axons from the chief 

 motor nucleus (Fig. 269). 



Distribution. From their origin the fibers pass forward through the 

 pons and emerge on its lateral aspect, forming the so-called small root of 

 the fifth nerve This then passes forward beneath the ganglion of Gasser, 

 leaves the cavity of the skull through the foramen ovale, and joins th< 

 inferior maxillary division already described. Its axons are ultimately 

 distributed to the muscles of mastication: viz., the masseter. the^ temporal, 

 the external and internal pterygoids, the mylohyoid, and the antenor portion 

 of the digastric. A few axons are also distributed to the tensor tympam and 

 tensor palati muscles. The efferent or peripherally coursing axons thus serve 

 to bring the nerve-cells from which they arise into relation with the mu 



f SticarConnections.--^ nuclei 'of origin of the small root are in 

 histologic and physiologic relation with the lower third of the motor area 

 of the cerebral cortex. Nerve-cells in this region give off axons which .enter 

 the pyramidal tract, descend through the internal Pg^*J^" 

 cerebri, after which they cross to the opposite side. Their end-tufts arbor- 

 ize around the cells of nuclei in the medulla oblongata. ^ 



Properties.-5/^/a/^ of the small root gives rise to convulsive move- 

 ments oJ the muscles of mastication. Division of the "^^^ 

 a Daralvsis of these muscles. Contraction or paralysis of the tensor tympam 

 ^d "S plti muscles would also be ^^^fffffSSi 



Functions. The function of the afferent fibers of the tit re is 



the transmission of nerve impulses from its P^"tS3KS3 

 the medulla oblongata; (b) through its afferent cortical tracts to the cereb ral 

 cortex where they evoke sensations. The nerve therefore endows all 



^e 1 flSon St^-^S^snussio, of nerve impulses 

 centrally with the nuclei of origin of the efferent ^^^JJg 



"Terijhlfstoulation of different areas in the distribution of the 

 afferent fibers eT, conjunctiva, nasal and oral mucous membranes teeth, 

 efc causes a Vafie'ty of reflex activities in the muscles associated with the 



