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Show 440 R. J. B. SUTTON ON HYPERTROPHY. [May 5, the adult, thus clearly showing that this animal originally possessed at least four teeth. After carefully reviewing these facts the conclusion forces itself upon me, that the modified dentition of this most singular animal has been attained by hypertrophy of its canine leading to atrophy of its less used companions ; but the original cause of the enlargement is as little known to us as is the cause of the asymmetry of its skull. There is probably no parallel to this in the animal kingdom-extreme hypertrophy, excessive atrophy, arrested growth, and malformation, exhibited in the dental armature of a single animal. Among remarkable teeth must be included those of Mesoplodon layardi. ° The illustration (fig. 7) represents the anterior part of the rostrum and lower jaw with the teeth of the extraordinary specimen of this Whale brought home by the ' Challenger' Expedition. The The rostrum of a Whale, Mesoplodon layardi, showing the singularly elongated and curved mandibular teeth. From the specimen obtained during the voyage of H.M.S. ' Challenger.' Figure taken from a cast in the Museum of the Royal College of Surgeons. drawing was taken from a model of the specimen in the Museum of the Royal College of Surgeons, London. The specimen is thus described by Prof. Turner in his ' Report on the Bones of the Cetacea':- "When I received from Mr. Moseley the lower jaw of the adult Mesoplodon layardi, only the left tooth was in its socket; the right had previously been extracted. The socket was situated at the junction of the symphysis with the body of the lower jaw, but more of the tooth was implanted in the body than in the symphysis. The length of the extracted tooth was 14 inches, G| inches of which had been included in the alveolus, or surrounded by the gums. The breadth of the tooth where it emerged from the alveolus was 3| inches. Each tooth consisted of a denticle proper and a strap-shaped shaft. The shaft was laterally compressed, and as it emerged from the socket it curved obliquely backwards, upwards, and inwards, so that its inner concave surface had been in relation with the sides and dorsum of the beak. As the summit of each tooth passed to the opposite side of the middle line, the two teeth crossed each other on |
