418 MABEL BISHOP 



mantle layer of the conjoined dorsal quadrants (figs. 10, 11)- 

 By analogy with the normal topographical relations of the 

 V-VII-VIII group of nerves, they suggest median acoustic 

 fibers. 



The caudal cranial nerve-mass, its associated nerves and fiber 



tracts 



IX, X, XI, XII. There is little to be said that is definite 

 concerning the nerve roots of the caudal cranial nerve mass. 

 Approximately the lower half of this mass is in fiber connection 

 with that portion of the median medulla which extends tongue- 

 like into the medullary canal. By this invagination it will be 

 recalled from the description of the gross anatomy of the brain 

 that the conjoined dorsolateral quadrants are toward the tip 

 of the 'tongue,' and are therefore narrow and tapering, while the 

 ventrolateral quadrants are broader and lie immediately ventral. 

 Into this distorted topography of the quadrants bundles of fibers 

 enter from the tangle of the nerve-mass only to become tangled 

 again in a confusion equally hopeless of clarification (figs. 12, 13). 

 However, by analogy meager understanding is possible. 



Attention has already been directed to the fasciculus longi- 

 tudinalis medialis on either side of the median raphe of each 

 head moiety (figs. 9 to 12). More caudally fibers of these 

 fasciculi may be followed dorsally along the sides of the forked 

 central canal of the medulla, i.e., into the median attenuated 

 dorsal quadrants (figs. 13, 14). Other fibers are seen to converge 

 toward the midline, or to merely tangle up within the median 

 area (figs. 13, 14). In the midhne of the fused dorsal quadrants 

 there is a sharply defined fiber tract which is probably a con- 

 joined tractus sohtarius (figs. 13, 14), and in the fused ventral 

 quadrants there is a rounded aggregation of cells and interlaced 

 nerve fibers that strongly suggests the motor nucleus of the 

 vagus complex (fig. 15). All intertangled among these fiber 

 tracts and embryonic cells are the root fibers of the cranial nerves 

 of the caudal cranial nerve-mass. 



