316 F. L. LANDACRE 



edge of the central ending, ganglionic relations, and peripheral 

 distribution of the various components of these nerves. Confusing 

 acustico-lateralis ganglia with communis or visceral ganglia or 

 failing to distinguish between perfectly discrete regions in the 

 brain leads only to confusion. The fact that in many types a 

 difference in size of fibres, in addition to the characteristics 

 mentioned above is present, has made possible the determination 

 of the exact composition of the trunks of the cranial nerves and 

 has made unnecessary the almost interminable and confusing 

 discussions of their homologies. The determination by Herrick 

 ('99) that there are in the Vth, Vllth, VHIth, IXth, and Xth 

 nerves of Ichthyopsida three, and apparently only three, chief 

 groups of sensory components and the exact definition and descrip- 

 tion of these components and their ganglia marks in a general way 

 the advance in our knowledge of cranial nerves since Strong's 

 paper appeared. 



The three components mentioned above are, first, the general 

 cutaneous, characterized by ending in the brain in the spinal 

 fifth tract, by having ganglia (in Menidia) in the Vth and Xth 

 nerves situated intracranially, by having medium sized fibres 

 and by being distributed peripherally to the skin as free nerve 

 endings. Second, the acustico-lateralis, or special cutaneous, 

 characte ^ized by ending in the brain in the tuberculum acusticum, 

 by having ganglia in the Vllth, VHIth, and Xth nerves, by hav- 

 ing large fibres and by being distributed to the ear and lateral 

 line organs only. Third, the communis or visceral sensory system 

 characterized by ending in the brain in the nucleus of the fasciculus 

 solitarius or its equivalent in the vagal, glossopharyngeal, and 

 facial lobes, by having ganglia in the Vllth, IXth and Xth 

 nerves, by having small sized fibres and by ending peripherally 

 in taste buds wherever found, and general mucous surfaces. 

 While this paradigm holds for teleosts generally, the irregularity 

 with which some of these components are distributed in the vari- 

 ous cerebral trunks makes it clear why there was so much con- 

 fusion and disagreement in the earlier attempts to determine the 

 homologies of these trunks. 



