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MR. J. B. SXJTTON ON HYPERTROPHY. 



[May 5, 



the adult, thus clearly showing that this animal originally possessed 

 at least four teeth. After cavefully reviewing these facts the con- 

 clusion forces itself upon me, that the modified dentition of this 

 most singular animal has heen attained by hypertrophy of its canine, 

 leading to atrophy of its less used companions ; Ijut 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 



Fig. 7. 



The rostrum of a Wliale, Mesoplodon layardi, showing the singularly elongated 

 and curved mandibular teeth. From the specimen obtained during the 

 voyage of H.JI.S. ' Challenger.' Figure taken from a cast in the Museum 

 of the Eoyal College of Siu-geous. 



drawing was taken from a model of the specimen in the ^Museum of 

 the Royal College of Surgeons, London. The specimen is thus de- 

 scribed 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 heen 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, 64 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 was3g 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 oblicpiely 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 



