BRIEF SKETCH OF THE TOOTHED WHALES. 85 



Toothed Whales, so that the only general features that call for 

 mention are the anterior limbs, which have the form of flattened 

 paddles — called flippers — in which the bones of the arm and 

 hand are covered with the dense integument without nails, the 

 absence of hind limbs and external ears. 



Whales may very naturally be divided into two great groups, 

 viz. the Whalebone Whales and the Toothed Whales {Delphinidce) , 

 whilst the Physeterine Whales (called after the Spermaceti 

 Whale), and the Ziphoids, also Toothed Whales, have an inter- 

 mediate position. These Toothed Whales are less specialized 

 than the Whalebone Whales, for in the latter whalebone 

 appears to be a peculiar development of the gum in animals 

 which formerly had teeth. Thus in the very young or embry- 

 onic whale (e. g. a Finner), teeth appear and afterwards dis- 

 appear in the jaw long before the whalebone grows, indicating 

 that the toothed condition is the primary, the brush-like 

 arrangement of whalebone the secondary, condition. 



This group (Odontoceti), while presenting teeth in most 

 instances (though in some there are none), as in other mam- 

 mals, yet exhibits certain aberrant features : in the asymmetry 

 of the skull,* the single external nostril, which is situated far 

 back and with peculiar knob-like nasal bones, the absence or 

 rudimentary condition of an organ of smell, the attachment of 

 the periotic to the skull (the tympanic not being ankylosed to 

 the periotic), the flattened plate of the maxillary, lachrymal 

 inseparable, the complex stomach, absence of a caecum (except 

 in Platanista), the aberrant condition of the hand, which, how- 

 ever, is pentadactylous, the nearly straight condition of the 

 halves of the mandible, the presence of true capitular processes 

 on several of the anterior ribs for articulation with the bodies 

 of the vertebrae, the division of the sternum into various pieces, 

 and the attachment to it of several pairs of ribs by carti- 

 laginous or ossified sternal ribs. 



* Lillie has lately attempted to account for the asymmetry of the Odonto- 

 cete skull by the position of the pipe-like continuation of the larynx, which, 

 instead of being in the middle line as in the Mystacocetes, is placed close to 

 the left wall of the pharynx (Proc. Zool. Soc, May, 1910, p. 781, text-figs. 

 73 and 74). Yet there is no asymmetry in the hyoidean skeleton of any 

 Odontocete. 



