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150 with the blow by which the Serpent inflicts its wound, the poison is at the same moment injected with force into the wound from the tip of the perforated fang.”

A singular exception to the general structure of the teeth occurs in a South African Snake (Deirodon, ), described by Dr. Andrew Smith, which is so interesting that we quote Professor Owen's description of the dentition and its use. The teeth are so small as to be scarcely perceptible; and are besides so soon liable to be lost, that the reptile has been described as toothless. The office assigned to this Serpent is to keep down the inordinate increase of the smaller birds, by preying on their eggs; and, as has been observed, the apparent defect in its dentition is in reality one of those beautiful instances of adaptation of structure to the exigencies of the case, to which every naturalist has so often to advert. “If,” says Professor Owen, “the teeth had existed of the ordinary form and proportion, in the maxillary and palatal regions, the egg would have been broken as soon as it was seized, and much of its nutritious contents would have escaped from the lipless mouth of the Snake in the act of deglutition; but, owing to the almost edentulous state of the jaws, the egg glides along the expanded opening unbroken, and it is not until it has reached the gullet, and the closed mouth prevents any escape of the nutritious matter, that the shell is exposed to instruments adapted for its perforation. These instruments consist of the inferior spinous processes of the seven or eight posterior cervical vertebræ, the extremities of which are capped by a layer