680 MAMMALIA [CH. 



finger has been greatly increased ; the limb is buried in the body 

 almost to the wrist. The terminal vertebrae of the tail have become 

 flattened and have expanded transverse processes (diapophyses). 

 These support a flattened tail fin which is extended in the horizon- 

 tal plane not in the vertical plane like that of true Fish. Whales 

 progress by moving the tail fin up and down, whereas in Fish the 

 movement is from side to side. 



All hair has disappeared, only one or two hairs being found in 

 the region of the lips in the embryo and these disappear when the 

 adult state is reached. 



The body is covered with a thick layer of fat termed blubber, 

 which preserves the heat of the body and thus in a different way 

 the Whale is as well protected against the cold water as is a Seal 

 which has retained its thick furry coat. It is for the sake of the 

 blubber which is used for making oil that Whales are principally 

 hunted now-a-days. The skull is distinguished by the great rounded 

 cranium and by the elongation of the bones of the face and jaws. 

 These support an immense prow-like snout formed chiefly of fat, 

 which is an admirable buttress of defence for the animal's skull. 

 The supra-occipital bone is of great size and forms the posterior 

 surface of the cranial dome, interposing between the small 

 parietals and meeting the frontals. The frontals develop great 

 orbital plates flanking the face, beneath which is the small orbit 

 bounded below by the slender jugal. The nasal organ has almost 

 totally disappeared : the vestigial nasal bones overhang an almost 

 vertical air passage which leads from the choanae to the external 

 nares. These latter open by a single opening termed the blow-hole 

 placed far back on the upper surface of the head. The epiglottis 

 and the arytenoid cartilages surrounding the glottis are prolonged 

 upwards into a kind of cone which is tightly embraced by a down- 

 ward prolongation of the soft palate : and thus the mouth can be 

 opened widely and enormous quantities of water taken into it, whilst 

 all the time air can pass uninterruptedly from the blow-hole to the 

 lungs and vice versa. When a Whale rises to the surface to 

 breathe, it empties its lungs by a strong blast just before it actually 

 reaches the surface, and in this way an ascending column of hot moist 

 air is produced. The moisture rapidly condenses into water, the 

 column seen from the deck of a ship looks like a jet of sea- water, 

 and in common parlance the Whale is said to " spout." In Whales 

 also the teats are situated far back, as they are in Cows, and the 

 connection of larynx and soft palate which enables the adult to 



