THE SKULL OF THE DUGONG, OR HALICORE.
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.