520 



Vertebrata. 



(6) The Hooded or Bladder-nose Seal (Cystophora cristata), -with 

 two upper, one lower incisor. Tlie male is characterised by the possession 

 of a flexible proboscis, which it dilates when angry. Polar seas. The 

 Sea Elephants (C. proboscidea) are somewhat similar forms. In the Indian 

 and Pacific Oceans, chiefly in the southern regions. 



Order 10. Cetacea (W/iales). 



The Whales are superficially much more like Pish than Mammals ; 

 as they have been completely adapted to an exclusively marine 



existence^ for which they are much better 

 suited than are other marine Mammalia 

 (Pinnipedia^ Sirenia). 



The body is piscine in form and pointed 

 at both ends; head, trunk, and tail, are 

 evenly continuous; externally there is no 

 trace of a neck; the tail is compressed, 

 extraordinarily powerful for a Mammal, 

 and very muscular. There is a horizontal 

 tail fin, a broad, stiff, bilateral ex- 

 pansion of skin, at the end of the tail. 

 Dorsally, there is usually a short, upright, 

 compressed dermal process, the dorsal 

 fin. The skin is smooth and shiny ; 

 hair and skin glands are generally wanting 

 in the adult, at most there are a few hairs 

 in certain regions of the head, especially 

 near the edges of the mouth ;* the dermis 

 is very thick, and contains an extraordinary 

 amount of fat (blubber). Lips are absent. 

 The anterior limbs only are well developed 

 (for the rudimentary hind limbs see below) ; 

 they are modified into stiff, clawless plates, 

 only movable from the shoulder; the 

 fingers are enclosed in a common skin, and 

 their limits are not recognisable externally. 

 The nares open high upon the head, and 

 are often united into a single aperture ; 

 the eyes are small; the external auditory 

 opening extremely small, and pinn^ are 

 wanting. The mammillae, one on each side, 

 are situated in pits near the anus. 



I'ig. 416. Eight anterior 

 appendage of a Pilot Whale. 

 H humerus, R radius, U ulna ; 

 s scaphoid, I lunar, c oimeiform ; 

 td trapezoid, u unciform ; I — 

 ir first to fourth fingers, V fifth 

 metacarpal. — After Flower. 



* Only some of the Mystacoceti (and a South American river Dolphin Inia) 

 have hairs when adult. On the other hand, the embryos of almost all Whales 

 (both Mystacoceti and Odontoceti) have a few hairs ; in the Odontoceti these only 

 occur above the upper jaw. 



