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Show 436 MR. J. B. SUTTON ON HYPERTROPHY. [May 5, minds, who never come across anything out of the common but they must rack their brains to find out some useful purpose for which they think the abnormal organ may be utilized, never considering for one moment the absurdity of the explanation. As is well known these teeth, like those of Rodents, grow from persistent pulps : if from any cause their growth is unopposed, as by want of antagonism between any two teeth, they grow to extraordinary length. In the case of the Babirusa it may readily be conceived that, from some cause or other, ihe upper and lower canines failed to come into apposition either by malformation or in a manner presently to be explained, and as a consequence grew enormously ; the abnormality frequently recurring, the peculiarity became transmitted to the offspring, eventually becoming perpetuated to such a degree as to become a common feature in the anatomy of the males of this particular species. Considered by itself, this isolated example perhaps does not carry much weight, but the condition may be approached insidiously from other specimens of the Suidae. The first stage may be observed in the Wild Boar (of which the dentition is represented in fig. 3, p. 437), where the form and direction of the canines are peculiar. The lower canine is slender when compared with the upper, is of some length, and plays against the front surface of the upper one, becoming pointed in consequence. The upper canine passes at first horizontally outwards with an inclination forwards. After clearing the outer lip, its apex becomes directed upwards and inwards, describing in its course a semicircle. A similar condition is seen in the Wart-hog, Phaco-chosrus aliani; but the second stage is presented by Phacochoerus athiopicus, in which the canine attains considerable proportions, as may be seen on reference to fig. 4 (p. 437). In the third step we are confronted with Babirusa, whose excessive canines I maintain are inherited pathological peculiarities resulting from want of apposition, probably brought about in the first instance as a result of malformation (see fig. 5, p. 437). It may, with reason, be asked, can an example be adduced of undoubted transmission of a pathological condition to the offspring so as to taint an entire community 1 An example offers itself in the so-called Tailless Trout of Islay. A careful and detailed account of this malformation is given by Prof. Traquair in the ' Journal of Anatomy,' vol. vi. p. 411. From this account it appears that the common Trout, Salmo fario, Linn., is frequently the subject of malformations, of which sigmoid distortions of the vertebral column and deficient development of the snout and jaws is the most common. In the present case, however, it is the caudal fin which is affected of all the Trout inhabiting a certain small lake. The most salient peculiarity of these Lochnamaorachan Trout is that the rays of the caudal fin are abnormally shortened, coarse at the extremities, and deficient as to the amount of dichotomization and number of the transverse joints ; besides which they also show a tendency to coalesce at their terminations. By the convergence downwards of the upper long rays and upwards of the lower ones, the fin assumes |