356 PHYSIOLOGICAL SERIES. 



this index in the same way for Balccnoptera sillahli, he 

 calculates it at between 0'2263 and 0'2680, i.e. as being 

 slightly below the average Carnivore and Ungulate status 

 Mini considerably higher than the average Rodent index. 



The apparently extraordinary dimensions of the Whale's 

 brain cannot therefore be considered an unusual pheno- 

 menon, because this enormous extent of cerebral cortex to 

 receive and " store " the impressions of such vast sensory 

 surfaces becomes a condition of survival of the animal. 



The marvellous complexity of the surface of the cerebrum 

 is the direct result of its great size. In order, apparently, 

 that the cerebral cortex may be efficiently nourished and 

 at the same time be spared to as great a degree as possible 

 the risk of vascular disturbances [such as would be pro- 

 duced by large vessels passing into it], its thickness does not 

 appreciably increase in large animals. Thus Dubois quotes 

 the following figures to show this : In a Whale (7 ////"'- 

 roodon) cortex 2-3 mm. (Kiikenthal and Ziehen), in />'< 

 2 mm., in Lepus 2 mm., and Homo 2-3 mm. Such being 

 the case, it naturally results that the increased bulk of 

 cortex in a large animal can only be packed by becoming 

 thrown into an increasing number of folds, separated by a 

 correspondingly large number of sulci. In Balcenoptera 

 this process is carried to a much greater extent than in 

 any other animal. 



(E. Dubois, Bull. Soc. d'Anthropologie de Paris, t. viii. 

 1897, p. 337.) 



The presence of a diminutive olfactory bull) and ;>e<ln 

 is a noteworthy feature which distinguishes the P>aleen 

 \\ 'hales from the Toothed "Whales, in which all the olfactory 

 stn:ctiires an- wanting. [In this specimen, unfortunately, 

 the olfactory regions are damaged.] According to (iuld- 

 berg the cerebral hemispheres and the two halves of thi 

 cerebellum are asymmetrical both in shape and si/e in 

 Balamoptcra musculus, but not in the other Baleen Whale-. 

 From the measurements of this >pecimcii there cannot be 

 much doubt that it belongs to the specie- " innm-ulits" and 

 yet the a-ymmctry, it' present, is so slight that it might 

 easily have occurred during the preservation of such a huge 

 mass of soft tissue. 



The so-called "fissure of Sylvius" is peculiar in that it 





