3gg John F. Holm 



elongated and extends from the acustic region deep down the Oblon- 

 gata, but I have not been able to trace any fibres into the spinal 

 cord either in stained or Golgi preparations. The manner of ending 

 is shown in Golgi preparations (Fig. 13 Fih.V^). 



This root is probably identical with the one described by Sanders 

 and homologous with the ascending root of the authors. The other 

 sensory root is found in a more dorsal region of the Medulla. On 

 arriving in the acustic region, part of the sensory fibres turn suddenly 

 in a dorsal direction, following the fibres of the dorsal root of the 

 Ramus anterior acustici until they both nearly reach the dorsal surface 

 of the brain (Fig. 12 F.V — VIII). Here these fibres as well as the 

 fibres of the Ramus posterior acustici turn dorsally and run caudally, 

 ending in the gray matter situated along the inner surface of the 

 restiform bodies and also probably in the Ganglion centrale superior 

 (Fig. 18). Haller (17) describes in Scyllium a ganglion in which 

 he thinks that sensory fibres belonging both to Acusticus and Trige- 

 minus end. He calls this ganglion the »large-celled Acustico-trige- 

 mino-nucleus« and states that it is situated in the exterior sensory 

 region, laterally to the dorsolateral tract. To homologise this nucleus 

 with any of the sensory nuclei described in Myxine is, however, a 

 matter of great difficulty, as the topographical anatomy of the brain 

 is so different in the two animals. Fibres from the Trigeminal tracts 

 are found to enter the Decussatio fibrae arcuatae internae and to cross 

 over to the opposite side of the brain, part of these fibres being, no 

 doubt, sensory, and entering the longitudinal tracts, but part of them 

 must be regarded as motor ones, as by the Golgi method I have found 

 cells in the motor region of the gray matter which send their processes 

 into the decussation and into the Trigeminal tracts (Fig. 11). Haller 

 (17) has found a similar arrangement in Salmo. Besides the decussating 

 motor elements the Trigeminus in Myxine has two motor roots, one 

 in the most rostral part of the Medulla, the other in the acustic 

 region, half way down the Medulla oblongata. The rostral nucleus 

 consists of a great number of cells (Fig. 10 and 20) situated laterally 

 of and close to the fourth ventricle. The cells are not large and 

 are generally of irregular or triangular shape (Fig. 10). Decussating 

 fibres of this root are found both rostrally and caudally of the fourth 

 ventricle. The caudal nucleus is found close to the lateral surface 

 of the brain, in the region of the acustic ganglion and consists of a 

 rather limited number of triangular cells, somewhat larger than most 

 of those of the rostral ganglion. 



