480 ZOOLOGY sect. 



The phalanges of the second and third digits always exceed in 

 number the number (three) normal in the Mammalia. The pelvis 

 is represented by a pair of horizontally placed styliform vestiges 

 of the ischia. Teeth may be absent and the mouth may be 

 furnished with sheets of haleen or "whalebone"; wheu present 

 the teeth may be very numerous and homodont, or less numerous 

 and heterodont, or reduced to a single pair. The epiglottis and 

 arytenoids are prolonged, and embraced by the soft palate, so as 

 to form a continuous tube for the passage of the air from the nasal 

 cavities to the trachea. The brain is large, and the cerebral hemi- 

 spheres are richly convoluted. The testes are abdominal. The 

 teats are two, and are posterior in position. The uterus is two- 

 horned, the placenta diffuse and non-deciduate (vide infra). 



This order includes the Baleen-Whales (Balcenidce), Sperm- 

 Whales (Physeter), Killers (Orca), Porpoises (Phoccena), and 

 Dolphins {Delphinus). 



Sub-order a. — Mystacoceti. 



Cetacea in which plates of baleen are developed. Functional 

 teeth are never present, and the premaxillse are narrow and take 

 only a small share in the formation of the rostrum. The nostrils are 

 situated far back. The nasal cavities are roofed over by the nasals. 

 The tympanic bones are scroll-like, and are fused with the periotics. 

 The rami of the mandible are not united anteriorly. 



This sub-order includes the Whale-bone Whales (Bcdmna and 

 others). 



Sui-order h. — Odontoccti. 



Cetacea in which the premaxilte are narrow, and the nostrils far 

 back, as in the Mystacoceti. The nasals are reduced and do not roof 

 over the nasal cavities. The tympanic bones are not scroll-like, 

 and do not become fused with the periotics. The rami of the 

 mandible are united at the symphysis. Baleen-plates are never 

 present, and teeth are developed and are usually very numerous 

 and homodont. This sub-order comprises the Porpoises (Phocana), 

 Dolphins (Belphinits and others), and Killers (Orca) ; the Sperm- 

 whales (Physeter and Cogia); the Bottle-nosed Whales (Hypero'ddon) ; 

 and Beaked Whales (Meso-ploAorC). 



Order 3. — Sirenia. 



Aquatic Eutheria with moderate-sized head and fish-like, de- 

 pressed, fusiform, body, with the pectoral limbs paddle-like, the 

 pelvic absent, and with a horizontally expanded tail-fin. There is 

 no vertical dorsal fin. There is a very thick wrinkled integument 

 devoid of or with only a scattered covering of hairs. The snout is 

 not greatly elongated, and the nostrils open by a pair of valvular 



