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The skull of this great Eocene sea-monster, in fact, shows by the narrow and prolonged interorbital region; the extensive union of the parietal bones in a sagittal suture; the well-developed nasal bones; the distinct and large incisors implanted in premaxillary bones, which take a full share in bounding the fore part of the gape; the two-fanged molar teeth with triangular and serrated crowns, not exceeding five on each side in each jaw; and the existence of a deciduous dentition its close relation with the Seals.
A constant uniformity in the structure and arrangement of the teeth is an important particular in the identification of species; and if any human race were found to deviate materially in its dentition from the rest of mankind, the fact would give rise to a strong suspicion of a real specific diversity.
Ibbetson saw a child with five incisors in the inferior maxillary bone, and Fanton-Touvet describes a young lady who possessed five large incisors of the first dentition in the superior maxilla. Rayer notes a case of dentition of four canines, which first made their appearance after pain for eight days in the jaws and associated with convulsions.
They thus constitute a grinding apparatus of great efficiency, and one which is repaired as fast as it wears, owing to the long-continued growth of the teeth. Some other peculiarities of the dentition of the horse must be noticed, as they bear upon what I shall have to say by and by.
In the "Musee de l'ecole dentaire de Paris" there are several milk-teeth, both of the superior and inferior maxilla, which are fused together. Bloch cites a case in which there were two rows of teeth in the superior maxilla. Hellwig has observed three rows of teeth, and the Ephemerides contain an account of a similar anomaly. Extraoral Dentition.
The specialization is of this kind. The true molars are those placed behind the molars having deciduous vertical predecessors. Now, as a dentition becomes more distinctly carnivorous, so the hindmost molars and the foremost premolars disappear. In the existing cats this process is carried so far that in the upper jaw only one true molar is left on each side.
Regarded systematically, the cerebral differences of man and apes are not of more than generic value; his Family distinction resting chiefly on his dentition, his pelvis, and his lower limbs.
But I must explain a little more at length what was the "typical dentition," that is to say, the exact number and form of the teeth in each half of the upper and the lower jaw of the early mammalian ancestor of lower Eocene times, or just before.
They thus constitute a grinding apparatus of great efficiency, and one which is repaired as fast as it wears, owing to the long-continued growth of the teeth. Some other peculiarities of the dentition of the horse must be noticed, as they bear upon what I shall have to say by and by.
Sometimes it is very prominent in man, as it is in most apes and many of the other mammals, and forms a sort of tusk. The apes of the Old World, or all the living or fossil apes of Asia, Africa, and Europe, have the same dentition as man. Skeletons of man and the four anthropoid apes. On the other hand, all the American apes have an additional pre-molar in each half of the jaw.
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