1885.] 



MR. J. B. SUTTON ON HYPERTROPHY. 



435 



With such an array of evidence no one would venture to deny 

 that the slender fourth and second metacarpals are rudimentary 

 structures in the true sense and meaning of that term. These bones 

 are often a nuisance to the animal, as they are exceedingly lial)le to 

 inflame and produce lameness ; the disease is known to veterinarians 

 as splent-bone, and often ends in osseous ankylosis between them 

 and the main metacarpal, a condition of things detrimental to the 

 Horse for working purposes. 



The history of this foot has been given, for it serves to illustrate a 

 principle — hypertrophy of one structure leading to the atrophy of 

 another; for in this case it seems the most probable view, that 

 gradual increase in the size and functional importance of the third 

 metacarpal bone has led to the abortion of the remaining bones, its 

 original companions, by causing a diversion of the nutrient stream to 

 its own advantage, but to the detriment of the lateral metacar|)als. 



r jvir 



12 3 15 6 



A series of figures to show the ancestry of tbemaniisof the modern Horse. 

 1. Oro/iip2nis (Eocene). 2. Mesohipjms (U)iper Eocene). 3. Miofiip- 

 ])us (Miocene). 4. Protohip2ms (Upper Pliocene). 5. Fliohijqms. 

 6. Equus (after Wiedersheim). 



In no structure is this principle so admirably ilhistrated or so 

 easily studied as in the teeth of mammals. Take, for example, the 

 curiously modified teeth of the Walrus ; we shall find the enlarged 

 and formidable incisors have for their companions some tiny func- 

 tionless teeth of no use whatever to the animal : as a rule they 

 quickly fall ; even when they persist, there are scarcely any sockets 

 provided for their reception. In this case it can hardly be denied 

 that hypertrophy of the canines has led to atrophy of the remaining 

 teeth. 



The Felidse supply us with similar examples. The large size to 

 which the canines attain in this group leads to atrophy of the 

 teeth immediately adjacent to them. This process seems, so far as 

 the Felidse are concerned, to have reached its culminating point in 

 the extinct Machcerodus, or Sabre-toothed Tiger, in which the 

 canines have attained considerable dimensions, whilst some of the 

 premolars iu the upper and lower jaws have disappeared. 



Let us now consider some other examples of hypertrophied teeth 

 somewhat different from the last. The extraordinary canines of the 

 male Bahirusa have afforded plenty of scope to those imaginative 



