SPERM WHALES AND BOTTLE-NOSED WHALES 257 



quite markedly from that of the whalebone whales. The upper 

 surface of the skull is always asymmetrical about its long 

 axis and the lower jaws are nearly straight, or with the two 

 halves closely united in front. The ribs, which in the whale- 

 bone whales are loosely connected with the backbone, in this 

 group are more firmly articulated. The number of digits in 

 the flipper is never reduced ; 5 are always present. 



SPERM WHALES. 



Family Physeterid^e. 



The family Physeteridae has two representatives, the Sperm 

 Whale and the Pigmy Sperm Whale. As the name of the 

 latter implies, the two differ considerably from one another in 

 size, but in other respects they have much in common. In 

 both genera functional teeth are restricted to the lower jaw, 

 which itself does not extend to the end of the snout. The single 

 blowhole is situated on the left side near the front end of the 

 head, and the spermaceti organ, a reservoir of transparent 

 oil lying above the bones of the fore part of the head, is 

 characteristic of both forms. 



Genus Physeter. 



THE SPERM WHALE (Physeter catodon). Fig. 67. 



The Sperm 'Whale or Cachalot is probably one of the best 

 known of all the Cetacea, and although in the past it was 

 identified by a considerable number of specific names, it is now 

 generally accepted that only one widely distributed species 

 called Physeter catodon exists. The name Sperm, a contraction 

 of Spermaceti, refers to the oil contained in the reservoir in 

 the front of the head, which used to be regarded as whale 

 spawn. The other common name, " Cachalot ", is from the 

 Gascon " cachau ", meaning a large tooth, and of course refers 

 to the row of conspicuous teeth on each side of the lower jaw ; 

 " catodon " also refers to the teeth, implying that they are 



