EVOLUTION AND EXTERNAL APPEARANCE 



79 



Figure 38. Left view of i ith-ijth lumbar and first caudal vertebrae of a Little Piked Whale, 

 from a skeleton in the Natural History Museum in Leyden. In this Aiysticete, the arterial 

 grooves run behind the transverse processes of the lumbar, and in front of those of the caudal 



vertebrae. {Slijper, igjG.) 



cleavage. Perhaps it will then become clear why in Odontocetes the upper 

 jaw protrudes over the lower jaw, and vice veisa in Mysticetes. 



The pectoral fins, the dorsal fin and the flukes of Cetaceans are almost 

 as streamlined as the wings of an aircraft. While the dorsal fin is well- 

 developed in some species, it is poorly developed in others such as the 

 Humpback and the Sperm Whale. In yet others (Grey Whale, Narwhal, 

 Beluga, Finless Black Porpoise) it is entirely lacking. 



Clearly the dorsal fin cannot play as important a part as it does in fish. 

 Now, fish have an air bladder situated well below the backbone. Its 

 position is such that the fish has a tendency to capsize and to float upside 

 down. Aquarium owners are quite fainiliar with this phenomenon - dead 

 fishes always float belly upwards. Cetacean lungs, on the other hand, lie 

 high up inside the body and there is little danger of capsizing, and hence 

 less need for a stabilizing fin. 



One of the prerequisites of good streamlining is smoothness of contours. 

 It has been shown that even the smallest projection has a measurable 

 adverse efTect on motion. For this reason, the door-handles of modern cars 

 and trains arc generally built in, i.e. they fit into the general contours. In 

 whales. Nature has seen to it that all those parts that are external in other 

 mammals are also 'built in'. Thus the penis lies within an abdominal fold, 

 and so do the mammae whose nipples are concealed in two slits on either 

 side of the female genital opening. There is no external ear, but then 

 aquatic animals do not need pinnae, which serve for collecting and 

 reflecting aerial vibrations. In their stead, the whale has small ear holes 

 flush with the surface of the body, halfway between the eye and the base 

 of the pectoral fin. In order to examine this aperture more closely, we 



