CEANIAL NERVES. 833 



fellow from the opposite side. The gray nucleus from which it arises is 

 the posterior part of the oculo-motor nucleus in the floor of the aqueduct 

 of Sylvius ; it also is connected with a gray nucleus in the part of 

 the floor of the fourth ventricle near to the origin of the fifth nerve. It 

 is a purely motor nerve and is distributed to the superior oblique muscle 

 of the eyeball. 



5. The Trifacial Nerve ( Trigeminus).— This is a mixed nerve, 

 arising, like the spinal nerves, from a motor and sensory root, the latter 

 being supplied with a ganglion (ganglion of Gasser). The anterior, 

 smaller, motor root arises in the motor trigeminal nucleus in the floor of 

 the fourth ventricle, which is connected with the cortical motor centre on 

 the opposite side of the cerebrum; there is also a descending motor 

 root from the corpora quadrigemina. The larger posterior sensory root 

 is connected with the sensory trigeminal nucleus at the level of the pons 

 with the gray matter of the posterior horns of the spinal cord as far as 

 the cervical vertebra, constituting the ascending root, and with the cere- 

 bellum through the crura cerebelli. This extensive origin of the sensory 

 fibres explains the great number of reflex relations of this nerve. 



After passing through the cranium the trifacial nerve divides into 

 three divisions — the ophthalmic, superior maxillary, and inferior maxillary 

 branches. 



The ophthalmic division, which receives fibres from the sympathetic 

 nerve, supplies sensory branches to the conjunctiva, lachrymal gland, 

 upper eyelid, brow, and root of nose, trophic fibres to the ej'eball, and 

 vaso-motor fibres to the dura mater and lachrymal gland. It is also the 

 afferent nerve for the reflex stimulation of the lachrymal secretion. 



The superior maxillary division supplies sensory nerves to the dura 

 .mater, to the angle of the eye, skin of temple and cheek, to the teeth in 

 the upper jaw, gums, periosteum, the lower eyelid, bridge and sides of 

 the nose and upper lip as far as the angle of the mouth, nasal chambers, 

 hard and soft palate. By receiving motor fibres from the facial (super- 

 ficial petrosal branch to Meckel's ganglion) it gives motor nerves to the 

 soft palate and uvula, and, receiving vaso-motor fibres from the cervical 

 plexus, it is the vaso-motor nerve for this entire region. 



The inferior maxillary division contains all the motor fibres of the 

 fifth nerve and supplies motor nerves to the muscles of mastication, the 

 tensor palati, and tensor tympani muscles. It also contains sensory fibres 

 which are distributed to the mucous membrane of the cheek, lower lip, 

 teeth, external auditory canal, and tip of tongue, the lingual branch being, 

 further, the special nerve of taste. This division also contains trophic 

 and vaso-motor fibres. 



6. The Abducens Nerve. — The sixth cranial nerve arises from the 

 emenentia teres in the fourth ventricle in front of and partly from the 



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