• xxvi Journal of Comparative Neurology. 



13. There is the closest agreement between the structure of the 

 cerebellum in Echidna and Omithorhynchus . The fact that in the for- 

 mer the floccular lobe is sessile, and in the latter pedunculated and en- 

 capsuled in a special bony case, is of Httle systematic significance, be- 

 cause such contrasts are not uncommon elsewhere among members of 

 the same family. [I have recently recorded an example of this in the 

 family of Anteaters, " The Brain in the Edentata," loc. cit.] 



14. The absence of 3. projecting corpus gem'culatum medi'ale, the 

 slight prominence of the iesfes, the (possible ?) diminutive proportions 

 of the lateral acoustic tubercule, and the fact that the corpus trapezoid- 

 eum is not a definite and compact bundle, all seem to point to a poorly 

 developed central (or cortical) auditory path in the Monotremata in 

 comparison with other mammals. 



15. It is impossible to say definitely whether the habits of life of 

 the animals, and the resultant diminution of visual acuity, are sufficient 

 to account for the dwindling of the corpus geniculatum laierale and the 

 flatness of the nates. 



We may safely say that every region of the brain in the Montre- 

 mata shows some peculiarity of structure which enables the observer 

 to distinguish it from the corresponding part of any other mammal, and 

 which indicates the wide gap which separates the Prototheria from the 

 Meta- and Eutheria. 



B. I. The presence of a definite pallium, which produces an in- 

 ternal capsule, crus cerebri, and pyramidal tract, and the existence of 

 a pons, indicate an advance beyond the Sauropsidan to a distinctly 

 mammalian status. 



2. The features A. 6, 8, and 9, mentioned above, are distinctly 

 Saurian, but the degree of elaboration of the hippocampal formation is 

 characteristically mammalian. 



3. The dwindling of the lateral parts of the cerebellum in the 

 Monotremata is a slight approximation to the Sauropsidian condition, 

 although the cerebellum in Monotremes is very much closer to the 

 mammalian than it is to the Saurian type. 



4. The diminutive size of the geniculate bodies and the smallness 

 of the testes in the Monotremata probably indicate that the latter have 

 not yet completely attained to the fully-developed mammalian position, 

 but retain some suggestions of the Saurian status. 



5. The olfactory bulb and nerve in Omithorhynchus afford a pe- 

 culiar instance of the persistence of the Saurian type. 



