238 



WHALES 



Figure 123. Skull of Boltlenose Dolphin with branches of the 

 fifth cranial nerve. The sensory fibres ramijv further in 

 the adipose cushion. {Hitber, 1^34.) 



love play. Like most other mammals, the dolphins in the aquarium like 

 to rub themselves against all sorts of rough surfaces including stones, 

 planks, and even tortoises. They like to have hoses playing on them and 

 delight in having their skins scrubbed with a brush, just as tame elephants 

 and rhinoceroses do. Although the skin of Cetaceans has not yet been fully 

 examined for tactile cells, the presence of a papillary layer in the corium 

 of the skin is evidence that the Cetacean sense of touch is well developed, 

 since, in many other mammals, tactile cells are particularly abundant in 

 these layers. 



The adipose cushion - or 'melon' - above the snout of Odontocetes 

 (see Chapter 4) is assumed to be especially sensitive, since it is provided 

 with a number of well-developed branches of the fifth cranial nerve (the 

 trigeminal nerve; see Fig. 123). These branches probably terminate in 

 tactile cells, but unfortunately their role awaits further investigation, 

 which may well show that, in them, Odontocetes have a special means of 

 registering water pressure and flow. Mysticetes, which lack a 'melon', 

 are provided with bristles on their upper jaw which, as we have seen in 

 Chapter 2, may very well serve as 'feelers'. 



The Japanese biologists Ogawa and Shida have, moreover, shown that 

 both upper and lower lips of Rorquals are provided with a great number 

 of small 'bumps', particularly at the tip of the snout. These bumps, which 

 have a diameter of about i mm., are said to contain a number of tactile 

 cells, which is borne out by the fact that the lips of whales have always 

 been known to be particularly sensitive. The tail and particularly the 

 flukes must be extremely sensitive as well, since dissections of the Cetacean 

 nervous system show the presence of very prominent nerves in these 

 regions. These nerves must have a sensory and probably a tactile function, 

 since there are practically no muscles in this region. Whether they do, in 

 fact, terminate in tactile cells is not known at present. 



All in all, we must agree with Jansen's contention (1950) that, together 

 with certain characteristics of the cerebellum, all the facts point to 

 Cetaceans having a well-developed tactile sense. 



