OCR Text |
Show 1885.] MR. J. B. SUITON ON HYPERTROPHY. 439 fisher, with thirty years' experience of this loch, has never taken but docked ones. It seems to me that these fish clearly inherit their deformity, and that it is a perpetuated pathological condition. Returning to teeth, there can be little doubt that a similar process has been at work modifying the singularly aberrant tusks of the Narwhal, Monodon monoceros. Its huge size, the curious spiral twist, undoubtedly correlated with the peculiar unsymmetrical condition of the facial portion of the skull found in this Whale as well as among other members of the Physeteridae, tend to support the notion of a pathological cause underlying these monstrosities. In this singular creature the adult male usually possesses a tooth growing from the left maxillary bone, in close relation with the maxillo-premaxillary suture and therefore regarded as a canine, which often attains a length of eight, nine, or even ten feet, with a basal diameter of four inches. The corresponding tooth of the opposite side usually undergoes development up to a certain point, and attains a size of six inches, but the pulp-chamber usually undergoes calcification before it has had time to make its way out of the alveolus, so that it remains concealed throughout the lifetime of the animal. Occasionally, however, this right tusk undergoes development, and equals in size the left one. Mr. J. W . Clark communicated to this Society in 1871 the results of an inquiry into the matter of double-tusked Narwhals, and has given in that very interesting paper details of no less than eleven bidental skulls of this Whale in different European Museums 1. This seems to afford evidence that normally the Narwhal should possess two teeth, but that from some cause or other the right one often remains suppressed in the alveolus ; and there is the significant fact, pointed out by Mr. Clark, that whenever a solitary tooth is present it is the left one, the right never being developed alone. The spiral twist in connection with these tusks always winds round them from right to left; if two tusks be developed, the twist of the spiral is in the same direction in both, as regards the skull right to left, whereas they appear unsymmetrical in respect to one another. There can be little doubt that this curious twist in the tusks is the effect of the same cause, whatever it may be, that produces the remarkable distortion in the facial portion of the skull of these whales. Prof. Flower has described, in the Trans. Odont. Soc. 1879-80, some curious Elephants' tusks contained in the Museum of the College of Surgeons. These tusks are spirally twisted, the twist possessing in some instances two or more turns: a deep groove extends from base to apex. In this instance it is clear that the malformation resulted from injury to the growing pulp when the tooth was in embryo. There is no just reason why the same line of argument should not be applied to the Narwhal tooth. The tusk has yet other interest for the pathologist. Professor Turner was fortunate enough to detect in the skull of a foetal Narwhal two rudimentary teeth, all traces of which are lost in 1 See P. Z. S. 1871, p. 42. 29* |