Hekrick, Gustatory Paths in Fishes. 447 



ed, retained its superficial position with reference to them. In 

 passing from the fishes to the mammals the fasciculus solitar- 

 ius has been crowded again somewhat laterally on account of 

 the further development of median structures. 



The short gustatory paths between the primary centers 

 and the motor nuclei of the oblongata by way of the substantia 

 reticularis are essentially the same in the fishes and mammals. 



The homology of the nucleus ambiguus of fishes and mam- 

 mals is not open to question. Forel in 1891 showed that the 

 so-called chief or dorsal sensory nucleus of the IX and X nerves 

 of mammals is in reality a motor nucleus of origin for these 

 nerves and much evidence in confirmation of this view has since 

 been published. The motor layer of the vagal lobe of cyprin- 

 oids corresponds in position exactly with this nucleus and is 

 probably in a broad way homologous with it, though of course 

 the homology is not exact. 



The long ascending secondary tracts from the vagal and 

 facial lobes (central gustatory path, or tractus secundus ascen- 

 dens) has not been identfied in any vertebrates save the fishes, 

 though it has long been in the minds of several neurologists 

 that the homologies of this tract are to be sought in the lateral 

 cerebellar tract of Flechsig (tractus spino-cerebellaris dorsalis, 

 Edinger). These fibers are known to arise from the cells of 

 Clarke's column (supposed to be a visceral sensory center) 

 and to enter the vermis cerebelli by way of the restiform body 

 of the same side. Dorsally of the ventricle they cross to the 

 opposite side and the whole arrangement strongly suggests a 

 survival of a primitive secondary tract from the visceral sensory 

 center of the spinal cord to the isthmus, to which in fishes the 

 strong secondary gustatory tracts arising in the oblongata are 

 added. This suggestion, however, cannot be taken seriously 

 until we have much more exact knowledge of the superior con- 

 nections of these fibers in the mammals and of the comparative 

 anatomy of the structures at the base of the vermis cerebelli. 



The morphological relations of the secondary gustatory 

 tract and nucleus are clearly defined. The tract represents a 

 specialization of the substantia reticularis alba and the nucleus 



