746 



MAMMALIA. 



possibly due to a duplication and separation of epiphyses. 

 The pelvis may exhibit a rudimentary ischium, with small 

 vestiges of femur and tibia. 



The rounded brain is relatively large, with well-convoluted 

 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 posterior 

 nares, and forms a continu- 

 ous canal, down which air 

 passes from nostrils to lungs. 

 The inspiration and expira- 

 tion 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 



ivj. /s'-'y* *- ^i* 1 -^ cm*-* m in-*. ***.-^ ~- ^p _ 



Greenland whale (Balcena). After puff Ot spray. 



Struthers. The kidneys are lobulated. 



p., Pelvis; /'., femur; T., tibia. The testes are abdominal. 



There are no seminal vesicles. 



The uterus is bicornuate. The placenta is non-deciduate 

 and diffuse. The two mammae lie in depressions beside 

 the genital aperture, and the milk is squeezed from special 

 reservoirs 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. 360. Pelvis and hind-limb of 



