CHAPTER XXX. 
CETACEANS,—continued. 
THE TOOTHED WHALES, OR ODONTOCETES. 
THE whole of the remainder of the existing Cetaceans form a group dis- 
tinguished from the preceding one by the absence of whalebone, and the presence 
of permanent teeth in at.least the lower jaw. This group, comprising existing 
families, is known as the Odontoceti, or Toothed Cetaceans, in contradistinction to 
the Mystacoceti, or Whalebone Whales. 
In addition to the presence of teeth, the group is also characterised by the 
following distinctive features. The two nostrils unite before they reach the surface, 
and thus open by a single aperture, which usually takes the form of a erescentic 
valvular shit placed transversely to the long axis of the head. In the skull the 
bones of the upper surface are arranged unsymmetrically on the sides; the nasal 
bones in existing forms being reduced to nodules, taking no share in roofing 
over the cavity of the nostrils. The two branches of the lower jaw are nearly 
straight, and of great vertical extent behind, while in front they come in contact 
with one another by flattened surfaces of larger or smaller extent, as is ordinarily 
the case among mammals. The ribs are more firmly jomed to the rest of the 
skeleton than in the whalebone whales, several of the anterior pairs articulating 
with the bodies as well as with the horizontal transverse processes of the vertebre, 
while below they are joined to the breast-bone by the intervention of so-called 
chest-ribs; the breast-bone itself usually consisting of several distinct portions, 
placed one behind the other. In all cases the flippers have five digits. 
SPERM-WHALES AND THEIR ALLIES. 
Family PHYSETERIDZ. 
The well-known gigantic sperm-whale is the typical representative of a family 
characterised by the total absence of any functional teeth in the upper jaw; those 
of the lower jaw being either numerous or reduced to a single pair. These characters 
are sufficient to distinguish the members of this family from those of the two others 
now existing, but it may be added that the skull is much elevated in the hinder 
region, so as to form a high prominence or crest behind the aperture of the nostrils. 
The members of this family include the largest of the toothed Cetaceans, and 
the whole of them are exclusively oceanic in their habits; their food consisting 
mainly or solely of squids and cuttles. 
