278 JoiTRNAL OK Comparative Neurology. 



the three tracts that are confined to the medulla are desig- 

 nated " tractus L," " tractus B,"' " tractus D." 



Tracius I^. — This is a short fasciculus which passes from 

 nidulus L directly laterad to the common root of the auditory 

 and facial nerves. 



Tractus B. — This fasciculus passes direct from the root 

 of the auditory nerve meso-dorsad to the eminentia acustica. 

 There it envelops nidulus B, after which it passes meso- 

 caudad to the raphe. This latter portion of the tract is 

 convex, with the convexity projecting caudad. A similar 

 tract is found in almost all vertebrate brains. 



Tractus D (Plate XVIII, Fig. 18). — This is a narrow 

 bundle which passes from the common origin of the auditory 

 and facial nerves mesad to the raphe. There it probably de- 

 cussates. This fasciculus appears to be the homologue of a 

 similar tract discovered by Professor C L. Herrick in the 

 alligator brain,(') a tract which he considers to be a fascicu- 

 lus of the facial nerve. 



There does not appear to be any very great resemblance 

 between the tracts of the auditory nerve of the birds and the 

 tracts of the corresponding nerve of the amphibia. Accord- 

 ing to Professor ()sborn,(') the eighth nerve of the amphibia 

 is composed of the following tracts: i . A tract from the pos- 

 terior longitudinal fasciculus, connecting with the myelon. 

 3. A tract from a large nucleus situated directly above the 

 exit of the ninth nerve and above the motor nidulus of the 

 trigeminal nerve. (This cell cluster is probablv Deiter's 

 nidulus.) 3. A tract from a small group of cells in the lower 

 angle of the metencephalon. 4. A tract from the fasciculus 

 communis. v ^ tract from the epencephalon. Certainly 

 the reseinblance is not very striking. Better preparations, 

 however, than those, at my disposal might strengthen the 

 homologies between these two groups, for occasionally I 

 have observed a faint indication of what might be a connec- 



1 Op. cit., p. 153. 



2 "Amphibian Brain Studies," p. 66. 



