File:Evolution and disease (1890) (14577555997).jpg

Identifier: evolutiondisease00blan (find matches)
Title: Evolution and disease
Year: 1890 (1890s)
Authors: Bland-Sutton, John, Sir, 1855-1936
Subjects: Diseases Medical genetics Abnormalities, Human Animals Disease Congenital Abnormalities
Publisher: New York : Scribner & Welford
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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Fig. 60.—A Frog (Raua iemporaria), with a supernumeraryfore-limb. attention in that it presents almost constantly adouble digit on the pes, increasing the number to five.This extra toe is due to dichotomy of the digit attachedto the vestigial first metatarsal ; it possesses threephalanges, and is furnished with a claw. This deviationfrom the number normal among fowls is further interest-ing in that it is transmitted truly to offspring when theDorking is crossed with breeds furnished with four toes. DICHOTOMY. 113 Dichotomy may, not infrequently, affect other digits;thus in fig. 61 a chick is represented with two bifidtoes and partial duplicity of the left leg. Birds withthese accessory parts may live and attain the adultcondition. Supernumerary legs are very common in birds, indeed
Text Appearing After Image:
Fig. 61.—A Chick with two dichotomized digitsand a supernumerary leg. almost every poultry breeder has seen examples, yetaccessory wings are very rare. One specimen only isknown to me, a dove, preserved in the museum of theRoyal College of Surgeons (fig. 62). This bird has anaccessory wing growing from the lower part of thesternum, 9 ii4 EVOLUTION AND DISEASE. The apparent rarity of supernumerary fore limbs, incomparison with hind limbs, will be dealt with whenconsidering the question of dichotomy as manifested inthe trunk. In cats and dogs dichotomy of the terminal segmentsof the fore and hind-limbs is fairly often seen, and afive-legged dog is one of the usual exhibits at a penny

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