The finer Anatomy of the Nervous System of Myxine glutinosa. 383 



the vertebrates, the ventral cornua being well marked but the dorsal 

 ones however indistinct (Fig. 23). A decussation of fibres is found 

 below the central canal and a horizontal section (Fig. 19) shows this 

 decussation in the caudal end of the Oblongata; it continues, increas- 

 ing in strength, towards the acustic region. The fibres themselves 

 are the Fibrae arcuatae internae. 



Both in stained preparations (Fig. 23) and in those made accord- 

 ing to the GoLGi method these fibres are seen to lead from the 

 dorsal sensory region of the Medulla into the Tractus tecto-spinales 

 et bulbores, some of them joining the tract situated close below the 

 central canal and known as the Fasciculus longitudinalis posterior. 

 This decussation, the »Decussatio fibrae arcuatae internae« is probably 

 indentical with the one in the acustic region described by Sanders 

 (41) as of fountain shape and which he believes connects the sensory 

 region with the central ganglion. AVhen dealing with the central run 

 of the Acusticus I will take this question into further consideration. 



Many distinct ganglia are found in the Medulla oblongata. The 

 ventral column of motor cells in the spinal cord can be traced up to 

 the level of the Vagus (Fig. 19) and laterally to this a large ganglion 

 is found close to the surface of the brain. This ganglion is called 

 the lateral-ventral ganglion by Sanders (41), who states, as before 

 mentioned, that it extends all along the lateral margin of the Medulla 

 oblongata from the entrance of the Trigeminus in front to that of 

 the Vagus behind in one continuous column of cells of various 

 thicknesses. This statement is entirely wrong. Both in transverse and 

 horizontal series of sections it is easily demonstrated that an inter- 

 vening space divides this row of ganglia into two groups, one caudal 

 of two nuclei and one rostral of three ditto. The further description 

 of these ganglia will follow in connection with their respective 

 nerves. In the basal part of the brain, below the Fibrae arcuatae 

 internae and close to the middle line, two pairs of celluuclei are 

 found, one caudal, the >Ganglion centrale nucleus posterior« situated 

 in the rostral end of the Medulla oblongata proper, the other rostral, 

 the »Ganglion centrale nucleus anterior« situated rostral ly of the 

 former and in a part of the brain which topographically belongs to 

 the Mesencephalon but which, judging by the embryological develop- 

 ment of Bdellostonia was ontogenetically a part of the Medulla 

 oblongata. Both these nuclei contain the largest cells met in Myxine, 

 specially the posterior nucleus, where 1 have found cells with a 

 diameter up to 75 a 80 /<. Above the »Ganglion centrale nucleus 



