This animal is allied to the Manati, both belonging to the order
_Sirenia_. They are water-living mammals. The dugong occurs only in
Eastern and Australian seas, the manati on the coasts of South America
and Africa. The grotesquely misshapen aspect of the skull of the dugong
is due to the enormous development of the bones in its upper jaw which
carry the cutting teeth (premaxillary bones and incisor teeth), and
its clumsy lower jaw. The former bear a tusk in the male, which in the
female is present but is never cut. There are no canine teeth, and in
the massive lower jaw no incisor teeth are ever cut. The rudiment of
one is, however, present in the jaw. It may be noted that the bones
carrying the upper incisors do not become united to those of the upper
jaw. The back teeth (chewing teeth), are only four, five, or six in
number in the dugong, whereas in the manati there may be twenty. A
remarkable tendency to vary in their dentition is characteristic of
this group of animals, and is no doubt in relation with differences in
food. A recently extinct member of the family (Steller’s sea-cow) had
no teeth at all, but masticated the soft sea-weeds on which it fed by
the aid of a horny palate (_Rhytina Stelleri_).
HEAD OF THE WART HOG (_Phacochœrus Æthiopicus_).
The Wart Hog is a native of Africa. His name makes reference to a pair
of wart-like excrescences, which are formed, one under each eye. These
may be an inch and a half in length.
There is an enormous development of the base of the zygoma. The incisor
teeth in the upper jaw are often wanting, and sometimes those in the
lower also. The snout is short and square. The so-called warts are
fleshy skin-growths and may be large enough to look like ears.
There is another Wart Hog (_Œliani_), met with in Abyssinia. It differs
from the Cape Wart Hog in that its incisor teeth in both jaws are more
persistent. It has two “warts.”
THE SKULL OF A PIG (_Sus scrofa_).
The skulls of most of the swine family may be recognised by the long
face, and the large size, in both jaws, of their dog-teeth or tusks.
These are especially large in the male sex, and are often curiously
curved, those of the upper jaw upwards, and those of the lower outwards
and upwards. The incisor, or biting, teeth vary very much in different
species and at different ages. They are often shed early, especially
those of the upper jaw. In some pigs the lower incisors are strong
and slope directly forwards, as if for digging. The incisor teeth
are of less service in the pig than in most animals, and are only
exceptionally used for biting or grazing. The pig makes great use of
the snout, and the nasal bones are strong and prominent. The molar
teeth are well adapted for chewing, and are usually worn flat on their
surfaces. Pigs champ but do not ruminate. They are, for the most part,
root-eaters. The rim of the orbit is always imperfect. The normal
dentition is three incisors, one canine, and seven molars in each
jaw. If the upper canine is extracted the lower one will grow into a
complete circle and reach the gum close to the root of the tooth. When
thus curved it forms an ornament much valued in Fiji.