CEREBELLUM, PONS, AND MEDULLA. 245 



nucleus in the central gray matter just posterior to that of the 

 third nerve (Fig. 107). The fibers pass dorsalward toward the 

 velum and make a complete decussation before emerging. 



The Fifth Cranial Nerve (N. Trigeminus). — This nerve arises 

 from the side of the pons by two roots, a small motor root, portio 

 minor, and a large sensory root, portio major. It is, therefore, 

 a mixed motor and sensory nerve, supplying motor fibers to the 

 muscles of mastication and sensory fibers of pressure, pain, and 

 temperature to the face, the forepart of the scalp, the eye, nose, 

 portions of the ear, mouth, and tongue, and to the dura mater 

 (Fig. 108). In the interior of the brain the motor portion, portio 

 minor, arises partly from a small nucleus in the pons and partly 

 from a long column of cells extending along the lower margin of the 

 central gray matter throughout the midbrain. This column and 

 the fibers arising from it constitute the descending motor root of the 

 fifth nerve (see Fig. 109). The sensory fibers originate from the 

 nerve cells in the Gasserian ganglion (g. semilunare). The branch 

 that enters the brain ends partly in a collection of cells in the pons, 

 the so-called sensory nucleus, and partly in a column of cells extend- 

 ing posteriorly throughout the length of the medulla. These cells 

 and the fibers ending in them constitute the descending spinal root 

 of the fifth nerve (see Fig. 109). 



The Sixth Cranial Nerve {N. Abducens). — This nerve arises from 

 the base of the brain at the posterior edge of the pons. It is a motor 

 nerve, and supplies fibers to the external rectus muscle of the eye- 

 ball. In the interior of the brain its fibers originate in a small spheri- 

 cal nucleus lying beneath the floor of the fourth ventricle. Con- 

 nections have been traced between this nucleus and the pyramidal 

 tract of the opposite side (Fig. 106). 



The Seventh Cranial Nerve {N. Facialis) . — This nerve appears 

 on the base of the brain at the inferior margin of the pons, lateral 

 and somewhat posterior to the emergence of the sixth nerve. It 

 is mainly a motor nerve, but carries some sensory fibers (fibers of 

 taste and general sensibility) received through the n. intermedins of 

 Wrisberg. The motor fibers of the nerve supply the muscles of the 

 face, part of the scalp, and the ear, including its intrinsic muscles, 

 and in addition secretory fibers are supplied to the submaxillary 

 and sublingual glands. Within the brain these fibers arise from a 

 conspicuous nucleus in the tegmental region of the pons lying 

 ventral to the nucleus of the sLxth, beneath the middle of the fourth 

 ventricle (Fig. 106). The sensory fibers of the nerve of Wrisberg 

 originate in the nerve cells of the geniculate ganglion. 



The Ninth Cranial Nerve (N. Glossophari/ngeus) arises from the 

 side of the medulla, — the restiform body. It is a mixed nerve, 

 supplying motor fibers to the muscles of the pharv^nx and the base 



