THE OBLONGATA AND THE NUCLEI OF THE CEANIAL NEKVES. 79 



reveals to which portion of the gray matter the lateral margin of our prepa- 

 ration eorfesponds. 



The anterior horns of the spinal cord are no longer clear in B; but 

 here, and even better in 0, note that iibers still arise from them. In section 

 A they have given oif the left cervical nerves functioning as Eypoglossus. 

 In C they send, also, dorsal motor fibers, which turn to make the motor 

 roots of the Vagus. The cell-column of the anterior horn remains intact 

 for a greater distance; higher up the motor fibers of the Facialis arise; also 

 those which join the Trigeminus. In the nucleus of the Facialis we have 

 probably to do with another cell-group than that in the nucleus of the 

 Vagus. 



Let us now turn to a more complicated section on which may be demon- 

 strated several of the especially important relations of the beginning of the 

 medulla. 



Fig. 41 presents a section through the lower end of the medulla of 

 GepJidloptera, a large ray. Note the ventral columns, or anterior horns, 

 from which arise nerves. The most anterior pair of cervical nerves, which 

 supply about the same region that in higher animals is innervated by the 

 twelfth pair of cranial nerves, — the Hypoglossus,- — arises Just like other 

 spinal nerves. 



The dorsal columns (posterior horns) are still to be seen, but it is 

 already difficult to trace their resemblance to the typical ones previously 

 described. They are much broader and changed to a looser, net-like, gray 

 substance, upon which rests a striking crescent-shaped nucleus (Fig. 41, 

 Fun. post.). The appearance of this long, trough-shaped structure, which 

 reaches far up under the eejebellum, is characteristic for the upper spinal 

 cord and the medulla. Higher magnification demonstrates that this note- 

 worthy nucleus receives along its whole course fine fibers from the surround- 

 ing mass of fibers; and when one follows them upward one can trace them 

 to the place where the Trigeminus cou.rses from the Gasserian ganglion into 

 the brain. Now, for the first time, one recognizes with what he is dealing: 

 a great fascicle from the sensory nerve, which passes from the ganglion 

 down into the cord to end in the above-described nucleus. This fascicle 

 is called the Radix spinalis Trigemini ; the nucleus at the end of the dorsal 

 horn is its terminal nucleus: Substantia gdatinosa Bolandt (Fig. 41, Nucl. 

 N. v.). On the median side of this nucleus lie fibers from the posterior 

 columns {Fun. post.). They inclose, in turn, gray masses, located where in 

 the cord the posterior columns lie, here called nuclei of the posterior col- 

 umns {nucl. fun. post.). In birds and mammals the existence of nuclei into 

 which a considerable part of the posterior columns enter is established 

 beyond doubt, as will be shown later; but in fishes and amphibia it is not 

 absolutely certain that a similar condition exists. In the Cephaloptera it is. 



