32 



CONARIO-HYPOPHYSIAL TRACT. 



CHAPTER II. 



CEREBEAL HOMOLOGIES IN VERTEBRATES AND 

 INVERTEBRATES. 



In a study of the homologies of the Divisions of the Vertebrate 

 brain with Nerve-centres in Invertebrates, the subjects of com- 

 parison should be the best-developed anterior and special-sense 

 masses in the latter and the least-developed ones in the former 

 subkingdom. 



In many Yi%\\Q^—Lepidosteus, Anguilla, e. g.* — the neural 

 masses in direct relation to nerves of special sense are as large 

 as, or larger than, those not so related bearing the names of 

 " cerebrum " and cerebellum," these being the hoinologues 

 of those centres which receive, in higher Vertebrates, such 

 vast accessions of grey and white neurine as to represent, or 

 seemingly compose, the whole organ known as the " brain " 

 in man and most mammals. 



The chief accumulation rises and expands from the parial 

 nerve-tracts or " crura " betw^een those portions of the tracts 

 which, in front of the cerebral hemispheres, develop the masses 

 or ganglia related to the sense of " smell," and those behind 

 the hemispheres related to the sense of " sight." Next in 

 retral succession are enlargements related to the sense of 

 " taste " and to movements of parts of the mouth ; behind 

 the " trigeminal " centres are those subserving the sense of 

 " hearing ;" above these centres rises the " cerebellum," 



Thus the central masses of the neural axis in relation to the 

 " special senses " run in longitudinal sequence from before 



* ' Anatomy of Yertebrates,' 8vo, vol. i. (1866), p. 275, figs. 174, 175. 



