No. 6. — CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY 

 OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD 

 COLLEGE, UNDER THE DIRECTION OF E. L. MARK. No. 141. 



Polydactylisiii in Man and the Domestic Animals, with especial 

 Reference to Digital Variations in Swine. 



By C. W. Prentiss. 



TABLE OF CONTENTS. 



Introduction . . 



I. Historical survey . . . . 

 II. Polydactylism in man . . 



A. Literature 



B. Observations 



III. Polydactylism in carnivora . 



A. Literature 



B. Observations 



IV. Polydactylism in the fowl . 

 V. Polydactylism in swine . . 



A. Literature 



B. Observations 



1. Manus in which the su- 



pernumerary digits are 

 independent of the nor- 

 mal digits 



a. One supernumerary 

 digit 



b. Two supernumerary 

 digits 



2. Manus in which tlie su- 



pernumerary parts may 

 be more or less closely 



PAOB 



245 

 246 

 251 

 251 

 252 

 255 

 255 

 257 

 259 

 261 

 2G1 

 263 



270 

 270 

 277 



connected with meta- 

 carpal II 



a. One supernumerary 

 digit 



b. Two supernumerary 

 digits 



C. Significance of variations 



observed 



VI. Polydactylism in ruminants 



A. Literature 



B. Observations 



VII. Polydactylism in the equidae 



A. Literature 



B. Observations 



VIII. Theories of polydactylism . 



1. External influences . . . 



2. Internal influences . . . 



a. Reversion 



b. Germinal variation . . 

 IX. Summary 



Bibliography 



Explanation of plates 



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284 



284 



285 



288 

 292 

 292 

 293 

 296 

 296 

 298 

 299 

 299 

 300 

 300 

 305 

 307 

 309 

 314 



Introduction. 



The frequent occurrence of extra digits on the extremities of both 

 man and the domestic animals has attracted the attention of many 

 anatomists during the past century. Various theories have been ad- 

 vanced to account for the appearance of these digital abnormalities, 

 and the opinions expressed by different investigators have been 

 remarkably contradictory, 



VOf.. XI,. — NO. 6 1 



