172 MAMMALIA ORDER VIII.CETACEA. 



horny growth takes place, however, after birth, young whalea having smooth 

 palates, with no trace of the horny plates. 



Apart from the presence of the distinctive and characteristic whalebone, 

 the members of the present group have the following characteristic features 

 in common. In the first place, the nostrils open externally by two distinct 

 longitudinal slits, or " blow-holes;" while the internal region of the nose 

 retains traces of an organ of smell this, by the way, being another proof 

 that cetaceans are descended from terrestrial mammals. Distinct, although 

 small, nasal bones partially roof over the nose-cavity of the skull ; and the 

 whole region of this part of the skull retains the normal symmetry. In 

 order to accommodate the whalebone, the two branches of the lower jaw are 

 curved outwards in a bow-like form ; while at their front extremities they 

 are only loosely connected together by ligament. The breast-bone, or 

 sternum, consists of only a single piece, to which but one pair of ribs 

 articulate ; and all the ribs have but a slight connection with the vertebra), 

 articulating only with the horizontal transverse processes, and not touching 

 the bodies of the vertebrae. Although the whalebone- whales are represented 

 by a comparatively small number of species, all these are of large bodily 

 dimensions, the smallest of them the pigmy -whale attaining a length of 

 some 20 ft. 



The most specialised representatives of the sub-order and family are the true, 

 or right-whales, constituting the genus Balcena, of which there appear to 

 be two well-defined species. Externally, the right-whales are easily recog- 

 nised by the enormous relative size of the head, the perfectly smooth throat, 

 the absence of a back-fin, and the moderate length of the flippers. Their 

 whalebone, which is black in colour, is proportionately longer and more 

 elastic than that of any other species, with the exception of the pigmy-whale ; 

 and for its accommodation the palate of the skull is much narrower and more 

 highly arched than in other whales, while the branches of the lower jaw are 

 more bowed outwards. The skeleton of the flippers contains five fully- 

 formed digits ; the vertebrre of the neck, which are reduced to the condi- 

 tion of thin plates, are completely welded together into a solid, immovable 

 mass, and the tympanic bone of the internal ear is squared. In conformity 

 with the arched form of the skull, the margin of the lower lip runs high up 

 on the sides of the head and is highly convex ; while the size of the opened 

 mouth is enormous. In spite, however, of the huge dimensions of this 

 cavity, the calibre of the throat is so small that it is a common saying among 

 sailors that a herring is sufficient to choke a whale. Of the two existing 

 species, the Greenland-whale (B. mysticetus) of the Arctic seas is the more 

 specialised, the head being larger and the whalebone longer than in its 

 southern cousin. The latter (B. australis) is commonly known as the 

 southern right-whale, and although formerly abundant in the Atlantic, is 

 nowadays a rare creature. From the right-whales the single species of 

 pigmy-whale (Neobalcena\ from the South American and Australasian seas, 

 differs in having a small, hooked back-fin, as it does in its white whalebone. 

 Whereas the Greenland species grows to a length of from 45 to 50 ft., the 

 pigmy- whale does not appear to exceed 20. A connecting link between the 

 right-whales and the under-mentioned rorquals is afforded by the great Pacific 

 grey-whale (Rhachianectes), in which the throat has a single fold, and the 

 back is devoid of a fin, while the whalebone is even shorter and more coarse 

 than in the rorquals, the palate showing but a slight degree of vaulting, and 

 the head being relatively small, and the body elongated. The vertebrae of 



