142 



Kewer fibres enter the fascicalus corDinunis th'io in either the 

 teleosts or the amphibi=ia3. 



The viscero-Tiotor nacleus gives origin to the motor fi- 

 bres of the V, VII, IX, and X nerves. The axones enter their 

 nerves chiefly through the medium of the fasciculus longituii- 

 nalis dorsalis. The nucleus receives impressions radiated from 

 the lobus vagi. 



The general cutaneous nucleus is the homologue of the dor- 

 sal cornu of the spinal cord. General cutaneous fibres, compo- 

 nents of the V, IX, and X nerves, terminate in both the substan- 

 tia gelatinosa and the deeper part of the nucleus. Many fibres 

 of the systen enter the spinal V tract for ultimate distribu- 

 tion in the spinal cord. 



The tuberculuTi acusticum is phylogenetically young. It 

 may have been derived from the structures of the dorsal cornu. 

 Pibres of tne acustico-lateral system terminate in the tubercu- 

 luTi acusticum. These are components of the VII, VII [, and X 

 nerves. Neurones are present in the tuberculum acusticum of 

 the molecular, granular, and Purkinje types, equivalent morpho- 

 logically to those of tne cerebellum. 



The Oerebellim is relatively large in Mustelus. This fact 

 is to be interpreted from the strong development of the sense of 

 equilibrium in the animal. The strictural plan of the cerebel- 

 lum is the same as that characteristic of higher vertebrates, 

 the differences being due to greater simplicity of detail. 



