THE CRANIAL NERVES AND THEIR NUCLEI 191 



1914; Brookover, 1914, 1917; Larsell, 1918, 1919). Since it was unknown at 

 the time the cranial nerves were first enumerated, it bears no numerical desig- 

 nation. 



I. Olfactory Nerve. Superficial origin from the olfactory bulb in the form of 

 a number of fine fila which separately pass through the openings in the cribri- 

 form plate. It is composed of special visceral afferent fibers with cells of origin 

 in the olfactory mucous membrane. The fibers terminate in the glomeruli of 

 the olfactory bulb. 



II. Optic Nerve. Not a true nerve; but both from the standpoint of its 

 structure and development a fiber tract of the brain. Superficial origin, from the 

 optic chiasma, or after partial decussation, from the lateral geniculate body, 

 pulvinar of the thalamus, and superior colliculus. Component fibers: special 

 somatic afferent exteroceptive; origin, ganglion cells of the retina; terminations 

 in the lateral geniculate body, pulvinar of the thalamus and superior colliculus. 

 The fibers from the nasal half of each retina cross in the optic chiasma. 1 



III. Oculomotor Nerve. Superficial origin, from the oculomotor sulcus on 

 the medial aspect of the cerebral peduncle. Composition: 



1. Somatic Efferent Fibers. Cells of origin, hi the oculomotor nucleus of the 

 same and to a less extent of the opposite side (Fig. 120). Termination, in the 

 extrinsic muscles of the eye except the superior oblique and the lateral rectus. 



2. General Visceral Efferent Fibers. Cells of origin in the Edinger-Westphal 

 nucleus. Termination in the ciliary ganglion, from the cells of which post- 

 ganglionic fibers run to the intrinsic nuscles of the eye. 2 



IV. Trochlear Nerve. Superficial origin, from the anterior medullary ve- 

 lum. Composed of somatic efferent fibers; cells of origin in the trochlear nucleus; 

 decussation in the anterior medullary velum; termination in the superior oblique 

 muscle of the eye (Fig. 120). 



V. Trigeminal Nerve. Superficial origin, from the lateral aspect of the 

 middle of the pons by two roots: the portio major or sensory root and the portio 

 minor or motor root. Composition (Fig. 120): 



1. General Somatic A/erent Fibers. A, Exteroceptive Cells of origin in the 

 semilunar ganglion (Gasserii), chiefly unipolar with T-shaped axons, peripheral 



1 It has been demonstrated by Arey that there are also efferent fibers in the optic nerves of 

 fishes which control the movement of the retinal elements in response to light, Jour. Comp. Neur., 

 vol. 26, p. 213. 



2 It is probable that the oculomotor, trochlear, and abducens nerves contain proprioceptive 

 fibers for the extrinsic muscles of the eye, but the cells of origin and the central connections of 

 these sensory components are unknown. 



