282 NEEVE-TISSUE. 



spindle-shaped ganglionic elements, and a layer of granules, the fibers between 

 which unite with those of the uppermost white medullary layer. 



The Origin of tlie Cerebral Nerves. As before stated, the tubular gray 

 matter, which is located around the aquseductus Sylvii and extends backward, 

 connecting with the floor of the fourth ventricle, gives rise to the cerebral 

 nerves. In this gray matter we find groups of multipolar ganglionie elements, 

 which are known to be the nuclei of the nerves. There are also exceptional 

 formations found in the tracts along the anterior pair of the corpora quadri- 

 gemina, which consist of very large globular ganglionie elements. These con- 

 stitute the sensitive roots of the trigeminus. Similar formations are found in 

 the anterior nucleus of the root of the auditory nerve. Brown and black pig- 

 ment granules are present in the substantia ferruginea of the fossa rhomboid- 

 alis and in the substantia nigra of the pedunculus cerebri. The nucleus of the 

 hypoglossal nerve has very large ganglionie elements and a reticular forma- 

 tion, produced by a close combination of layers of the gray and white sub- 

 stance. In the medulla oblongata such formations occur : in the pyramis, in 

 the fasciculi restiformis, gracilis, and cuneiformis. 



The olfactory nerve arises from the olfactory bulb ; its external and larger 

 tract is connected with the gyms uncinatus or subiculum cornu Ammonis ; 

 its internal tract connects with the frontal extremity of the gyrus fornicatus, 

 and its middle tract with the head of the corpus striatum. 



The optic nerve very probably starts from several nuclei, one of which is, 

 perhaps, the anterior pair of the corpora quadrigemina (Corp. bigem. super.). 



The motor oculi and troclilear nerve spring from a cylindrical group of ele- 

 ments below the aquseductus Sylvii, near the median line. This nucleus, by 

 means of nerve-bundles, is in connection with the corpus striatum and the 

 corpus bigem. superius. 



The trigeminus nerve has several nuclei. The upper sensitive nucleus is 

 composed of groups of ganglionie elements along the tegmentum of the ante- 

 rior pair of the corpora quadrigemina ; the middle sensitive nucleus is located 

 below the upper one ; the under sensitive nucleus exists in the medulla 

 oblongata, and is traceable into the posterior column of the spinal cord. The 

 motor root of this nerve has its nucleus in the fossa rhomboidalis, extending 

 anteriorly to the aquseductus Sylvii. 



'The abducent nerve originates from a nucleus in the anterior portion of 

 the fossa rhomboidalis, and is in connection with the deeper situated nucleus 

 of the facial nerve. 



The facial nerve originates from three roots arising from a nucleus in the 

 depths of the floor of the fourth ventricle, where large ganglionie elements 

 with bulky offshoots are seen. 



The auditory nerve has its nucleus in the floor of the fossa rhomboidalis, 

 extending from the median line toward the pedunculi cerebelli, and gaining in 

 thickness as it advances. The median portion is the inner acoustic nucleus, 

 which may be divided into three parts. The broad outer portion has large 

 pyramidal ganglionie elements. An anterior nucleus is located at the side of 

 the peduDculus cerebelli. 



The glosso-pnaryngeal and vagus nerve arise from one common nucleus, the 

 anterior portion of which, reaching the internal acoustic nucleus, belongs to 

 the glosso-pharyngeal nerve, while the posterior portion, in the ala cinerea of 

 the fossa rhomboidalis, constitutes the vagus. 



The spinal accessory nerve originates partly from the nucleus of the vagus, 



