SENSES AND THE CENTRAL NERVOUS SYSTEM 245 



the tongue. In the next chapter we shall see how minor is the part these 

 muscles play - hence their smallness. The remaining cranial nerves show 

 no special modifications and we shall therefore pass over them in silence. 



The cerebellum, on the other hand, is so unusual that we shall discuss 

 it at some length. The weight of the cerebellum of adult Rorquals is about 

 1,300 grams (29 oz.), i.e. about the total weight of the human brain. Now 

 these figures, in themselves, tell us little. The picture becomes clearer 

 when we learn that the weight of the cerebellum accounts for 20 per cent 

 of the total weight of a Rorqual's and other Mysticete's brains, and for 

 15 per cent in Odontocetes, while it accounts for only about 10 per cent 

 of the brain of terrestrial mammals. This is not at all strange, however, 

 since the function of the cerebellum is primarily the control of voluntary 

 movements. Hence it is always large in agile animals. The lower per- 

 centage of the Odontocete cerebellum is not due to a minor development 

 of this part of the brain but to the very extensive development of the 

 cerebrum. 



An examination of the Cetacean cerebellum immediately shows that it 

 is as highly convoluted as the cerebrum, the white matter being more 

 highly ramified than it is in any other mammal, man included. In 1950, 

 when J. Jansen, a scientist attached to the Anatomical Institute of the 

 University of Oslo, compared the sizes of various Cetacean lobes with that 

 of other mammals and of man in particular, he came across very striking 

 differences. The enormous development of the lobulus simplex is 

 undoubtedly connected with the high stage of development of the tactile 

 nerves and is further evidence that the tactile receptors may be sensi- 

 tive to water pressure and flow to which the body must respond. The 

 poor development of the lobus ansiformis is associated with the fact that 

 Cetacean limbs have undergone considerable reduction and the remark- 

 able size of the paraflocculus is due to the role it plays in muscle co- 

 ordination, a phenomenon to which the great Dutch anatomist Bolk 

 drew attention as early as 1906. 



Before discussing the Cetacean cerebrum, we must first look at the total 

 weight of the brain which it largely determii:ies. Now, Cetacean brains 

 have been weighed on many occasions, the highest recorded figure being 

 the brain of a Sperm Whale which weighed 19-6 lb., i.e. the weight of an 

 eight- to nine-month old baby. The record for the brain of a Fin Whale is 

 18-3 lb., for that of a Humpback Whale (average weight 1 1 lb.) is 15 lb., 

 and the brain of a 100- ton Blue Whale was found to weigh about 151 lb. 

 The brains of the other big whales have still to be weighed, but these four 

 may be said to have larger brains than all other mammals. An elephant's 

 brain has a maximum weight of 1 1 lb., and the terrestrial mammal with 

 the second biggest brain is man (total brain-weight about 3 lb.). The 



