. Evolution and disease . Fig. 133.—The head of a Sheep with a large wart-horn on itshead. and hare. I have recently seen one growing near thehock of an eland : in birds they have been recorded in theparrot, greenfinch, linnet, canary, and museum of the Royal College of Surgeons, London,contains an admirable collection of such horns, one ofthem which grew from the flank of a ram, and from itsstructure is clearly a wart-horn, is the largest on record, 270 EVOLUTION AND DISEASE. it measures in length nearly one metre, and is twenty-eight centimetres in circumference at the bas
. Evolution and disease . Fig. 133.—The head of a Sheep with a large wart-horn on itshead. and hare. I have recently seen one growing near thehock of an eland : in birds they have been recorded in theparrot, greenfinch, linnet, canary, and museum of the Royal College of Surgeons, London,contains an admirable collection of such horns, one ofthem which grew from the flank of a ram, and from itsstructure is clearly a wart-horn, is the largest on record, 270 EVOLUTION AND DISEASE. it measures in length nearly one metre, and is twenty-eight centimetres in circumference at the base. In birds cutaneous horns grow very rapidly, and areshed with each moult: in the course of three monthssuch horns have been known to attain a leneth of seven. Fig. 134.—The head and leg of a Thrush : the horns on theleg arise from warts, that on the head from a sebaceouscyst. and even ten centimetres, and to be reproduced forseveral consecutive years. An excellent specimen of thisform is shown on the thrush (fig. 134). This bird wasobserved by Mr. Roger Williams : it had three wart hornson the legs, and upon its head a sebaceous cyst with a ZOOLOGICAL DISTRIBUTION OF DISEASE. 271 cutaneous horn just commencing to protrude from bird is interesting as iUustrating the two modesby which these horns arise. The statement that birdshave no sebaceous glands except the uropygial glandrequires modification. Cutaneous horns, due to the hardening of secretion,occur as normal productions in several animals. Thusthe patch of spines on the fore-arm of hapalemur{H. griseus) and on the fore-arm of the ring-tailed lemur{L. catta), are of this character. Even more curious arethe wart-like processes formed on the skin of the thighin lizards, from the
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectabnormalitieshuman
