24- 



WHALES 



Figure 125. Longitudinal section through the brain of a Bottlenose Dolphin. Photograph: 



G. E. Pilleri, Bern. 



Before discussing the convolutions of the Cetacean brain in greater 

 detail, we must first look at the general function of their brain. We have 

 already seen that Odontocetes lack an olfactory nerve, though vestiges 

 of it can be found in Odontocete embryos and in adult Sperm and Bottle- 

 nose Whales, the latter having a small perforation in the ethmoid plate. 

 But in all these animals the olfactory sense is practically non-existent, and 

 we may therefore take it that the olfactory centres of the brain itself would 

 hence be absent or atrophied. In fact, we find that the mammillary body, 

 the anterior nuclei of the thalamus, and the hippocampus are absent. 

 On the other hand, it appears that some parts of the brain which have 

 always been considered as olfactory centres - e.g. the amygdaloid nucleus 

 and the olfactory tubercle - are fairly well developed. We may therefore 

 agree with Breathnach, who published comprehensive papers on this 



