142 PHYSIOLOGICAL SERIES. 



of mistaking it for the pons. On the left side of the 

 sjM-eimen (fig. 35, V.M.) this motor root has been cut short. 



The other cranial nerves conform to the usual mammalian 

 plan, which is seen to hetter advantage in the brains of 

 other animals (ride infra). 



Perhaps the most inexplicable feature of the brain of the 

 Platypus (as also of the Spiny Anteater) is the relatively 

 large size of the so-called " pallium " of the cerebral hemi- 

 sphere. The term "pallium " is at the present time used 

 in a perplexing variety of ways by different writers, and 

 all of these applications of the term are strangely at variance 

 with that which Reichert intended to convey when he in- 

 troduced the word " mantle " or " pallium/' There are 

 three distinct varieties of mantle in all mammalian hemi- 

 spheres: a basal pallium or pyriform lobe, a marginal 

 pallium or hippocampus, and a more variable area inter- 

 calated between these two regions, which has hitherto 

 received no exclusive title. To indicate this region I shall 

 employ the distinctive, if hybrid, name " neopallium " *. 

 Among lowly-organised mammals there is, according to 

 Dubois, a more or less intimate relationship between the 

 size of this cortical area and the extent of the various 

 sensory surfaces of the body. In the case of the Platypus, 

 in which the visual apparatus is very poorly represented 

 and the auditory nerve is not remarkable for its large 

 size, one naturally looks to the enormous trigeminal nerve 

 for the explanation of the large neopallium. But that this 

 cannot be regarded as the full explanation is shown by the 

 still more obtrusive greatness of the neopallium in the 

 Spiny Anteater, in which the trigeminal nerves are not 

 extraordinarily large and none of the other cranial nerves 

 attain to exceptionally great dimensions. As one i-. 

 naturally loathe to explain this large neopallium as ana- 

 logous to that of the Primates, in which the neopallium 

 becomes enlarged and elaborated out of all proportion to 

 the extent of the sensory areas in association with the 

 development of the higher psychical faculties, a satisfactory 



* Journ. Anat. & Phys. 1901, p. 431. 



