Herrick, Criteria of Homology. 209 



in spite of the admixture of facialis fibers tlirough the chorda tympaiii, 

 provided the trigeminal element can be sho^vm to be phylogenetically 

 the older. 



The principles outlined above for guidance in determining homol- 

 ogies in the peripheral nervous system can be applied, mutatis 

 mutandis, to tracts within the central nervous system. It will not 

 be necessary to make the application here in detail. The treatment 

 of the grey nuclei and correlation centers Avill also be controlled 

 by similar rules, the aim being to homologize only such structures 

 as are genetically related and to use functional cormections wherever 

 possible as guides to homology. 



