MAMMALS. 



409 



includes large and medium-sized whales with toothless upper jaws-. 

 Physeter, which includes the sperm whales, dates from the pliocene of westerm 

 Europe and South Carolina. It has numerous (20-25) conical teeth in the: 

 lower jaw. The head is high, truncate in front, and in the ' chair ' betweem 



FIG. 375. Pigmy whale, Kogia floweri, from Gill. 



the cranium and snout occurs a thick waxy oil, the spermaceti. The sperm 

 whale (/'. macrocephaltts) furnishes the ambergris which is really imperfectly 

 digested squid become concretionary in the intestines. Ziphins includes the 

 two-toothed whales, so called from the existence of but a pair of teeth in the 

 lower jaw. Allied are Hyperoodon, the bottle-nosed whales, Mesoplodon, and 

 the pigmy whales, Kogia. 



SUB-ORDER 3. MYSTA- 

 COCETI (BAL^NOIDEA). 



Skull symmetrical ; two 

 nostrils at the base of 

 the snout ; temporal fossae 

 short ; functional teeth lack- 

 ing, the upper jaw bearing 

 plates of baleen ; most of 

 the ribs with a single head ; 

 sternum broad, in one piece, 

 and articulating with the 

 first pair of ribs alone. 



The whalebone whales 

 have teeth in both jaws in 

 the foetal stage, but these 

 never pierce the gums, and Fm ^ Cross . section through the jaws of a 

 are absorbed before birth. whalebone whale> after Delage . Bones black; w> 

 After birth a series of flat- wha l e bone, hanging down into the cavity of the 

 tened plates of horny mate- mou th, m ; c, ethmoid ; mx, maxillary ; p, parietals ; 

 rial make their appearance v , vomer. 

 on either side of the upper 



jaw. These plates, of which there are several hundred pairs, are triangular 

 in shape, with the inner edges fringed out into hair-like fibres, the plates being- 

 at right angles to the axis of the body, and the whole forms a very efficient 

 straining-apparatus, by means of which the whales separate the small animals. 

 On which they feed from the surrounding water. Morphologically the baleen 



