The order Cetacea has been divided into two very natural groups—the Whalebone Whales, Mystacoceti, and the Toothed Whales, Odontoceti.
The former are characterized by the absence of teeth and the possession in lieu thereof of great plates of horny fibre, called "baleen," depending from the palate, and known as the "whalebone" of commerce. The latter are destitute of whalebone and possess teeth, either in one jaw or both, sometimes few and rudimentary, sometimes numerous, and always single-rooted and similar to one another.
Again, the Whalebone Whales possess olfactory organs, and have a double orifice to the blow-hole; the ribs are very slightly articulated to the vertebrae, and the sternum or breastbone consists of a single piece, which is attached to the first pair of ribs only.
The Odontoceti, or Toothed Whales, on the contrary, have no olfactory nerve; a single external orifice to the blow-hole; the anterior ribs more closely united to the vertebrae; and the sternum, which, in the young at least, is composed of several segments, is attached to several of the ribs.
The first group, Mystacoceti, may be conveniently divided into two families—the Balænidæ, to include the Right Whales; and the Balænopteridæ, to include the Hump-backed Whale and the Rorquals, or Fin Whales.
The second group, Odontoceti, have been divided by Professor Flower into three families—the Physeteridæ, to include the Cachelots and Ziphioid Whales; the Platanistidæ, for the reception of the long-snouted fresh-water Dolphins of India and South America, of which we have no representatives in our waters; and the Delphinidæ, to include the Dolphins and Porpoises, with the Narwhal, and the White Whale, or Beluga.
The following Table will convey some idea of the number and variety of the British Cetacea, and will at the same time exhibit, to a certain extent, their affinities. The nomenclature adopted is, with a few exceptions, where older names seemed to deserve priority, that of the second edition of Bell's ' British Quadrupeds,' in which work will be found much useful information on the subject of British Whales and Dolphins, and, by way of introduction, an excellent account of their organization.
