60 PROCEEDINGS OF THE ACADEMY OF [1887. 



A PRODROME OF A MEMOIR ON ANIMAL LOCOMOTION. 



Emeritus Professor of Physiology in the University of Pennsylvania, 

 The writer has undertaken at the request of the representatives 

 of the University of Pennsylvania a series of studies on animal 

 locomotion. The subject has been approached from the point of 

 view presented by instantaneous photography, and has been espec- 

 ially based on the results obtained by Mr. Eadweard Muybridge. 

 The writer desires in this connection to return his acknowledg- 

 ments to Mr. Muybridge for opportunities in examining early 

 impressions of the plates, which he is engaged in publishing under 

 the auspices of the University, and also to state that he is indebted 

 to Prof Thomas Eakins for facilities afforded in studying the results 

 of an experiment in the use of a modified form of Marey's wheel, 

 devised by him in photographing the action of the horse in motion. 

 This short paper embraces the points which have been thought to 

 have sufficient interest to appear in advance of the final memoir, 

 and will include observations on the movements of the quadrupeds 

 only. 



Many of the statements could have been deduced fi*om data 

 already accessible to the Avriter. But since he wrote the paper 

 immediately after the inspection of the photographs his conclusions 

 may be said to be based upon them. At the same time he has not 

 hesitated to include materials not embraced by the photographs. 

 Whenever practicable the study of a given series was carried 

 on at the same time that the animal itself lay dissected before 

 him. For example, when studying the j)hotographs of the 

 elephant he had the good fortune, through the courtesy of Prof, 

 Huidekoper, to dissect the limbs of an elephant. He has also dis- 

 sected^ the horse, the ox, the raccoon, the sloth, the skunk, the 

 Virginian deer and the domestic cat, 



THE USE OF TERMS. 



It is necessary to propose the use of a few terms which will clearly 

 express in a word a meaning which otherwise would require the 

 employment of a cumbersome phrase. The words flexion, extension 



1 In this connection the writer wishes to give especial acknowledgments to his 

 friends Prof. Horace Jayne and Mr. Edwin A. Kelly. 



