CETACEANS 



863 



The rounded brain is relatively large, with well-con- 

 voluted cerebral hemispheres. 



As to the alimentary system — salivary glands are rudi- 

 mentary or absent, the stomach is chambered, the intestine 

 has rarely a caecum, the liver is but slightly lobed, there is 

 no gall-bladder. 



The heart is often cleft between the ventricles. Both 

 arteries and veins tend to 

 form retia mirabilia. 



The larynx is elongated, 

 so that it meets the pos- 

 terior nares, and forms a 

 continuous canal, down 

 which air passes from nos- 

 trils to lungs. The inspira- 

 tion and expiration occur 

 at longer intervals than in 

 terrestrial mammals. The 

 water-vapour expelled along 

 with the air from the lungs 

 condenses into a cloud, 

 which is sometimes in- 

 creased by an accidental 

 puff of spray. 



The kidneys are lobu- 

 lated. The testes are ab- 

 dominal. There are no 

 seminal vesicles. The uterus 

 isbicornuate. The placenta 

 is non-deciduate and diffuse. 

 The tw^o mammae lie in de- 

 pressions beside the genital 



aperture, and the milk is squeezed from special reser- 

 voirs into the mouth of the young. Usually a single 

 young one is born at a time, and there are never more 

 than two. 



All are carnivorous ; but, while many feed on small 

 pelagic animals, others swallow cuttles and fish, and Orca 

 attacks other Cetaceans and seals. Most are gregarious, 

 and live in schools or herds. 



Fig. 512. — Pelvis and hind-limb 

 of Greenland whale {Balccna). 

 — After Struthers. 



P., Pelvis ; F., femur ; T., tibia. 



