WORK OF THE PHYSIOLOGICAL STATION AT PARIS. 407 



anatomical facts aud experimental determinations. And since we are 

 considering here only the comparative physiology of animal locomotion, 

 1 believe that it is easy to point out the successive stages which ought 

 to lead to this result. 



First, the animal forms should be grouped according to the type 

 of motion pecuhar to them, so as to bring into notice their general 

 anatomico-physiological relations. This we have now begun to do, and 

 it IS already evident that many of these relations depend upon ordinary 

 laws of mechanics. These rehite to muscles, bones, and articular sur- 

 faces. As regards this I can only summarize here what I have given 

 elsewhere with more detail.' 



The relation existing between the form and the functions of muscles 

 is as follows: The extent of the movement of a muscle is in proportion 

 to the length of its red fibers; its force is proportional to the cross- 

 section of such fibers; the work it can i^erform is proportional to its 

 weight. 



These relations, the first of which was established by Borelli, can 

 easily be verified upon the muscles of a single animal. They explain 

 also why, in two different species, homologous muscles have diiferent 

 anatomical characters; it is because the functions of the muscles difier 

 in tlie two si^ecies. 



It will be seen that in order to carry further the anatomico-physiolog- 

 ical relation it will be necessary to determine with great precision the 

 functions of each muscle and the peculiarities of its movements; it is 

 precisely for that purpose that the experiments have been undertaken 

 which I have cited above. 



The form and length of the bones correspond to that of the muscles 

 attached to them, and to which they seem subordinated, as is shown 

 by the beautiful expo'iments of Fick ; the configuration of the articu- 

 lations shows the character of the movements which they permit. 



Let us consider, for example, the form of the head of the humerus in 

 different animals. We see that it has a spherical curvature in man, 

 monkeys, and lemurs, in which animals movements in every direction 

 are allowed; that it is cylindrical in ruminants and pachyderms whose 

 anterior limbs move backward and forward, parallel to the axis of the 

 body; elliptical in birds whose wings move with unequal amplitude in 

 two directions perpendicular to each other. It is impossible not to see 

 that there is, between the form of the articular surfaces and the move- 

 ments, a necessary relation which permits us, when we know the char- 

 acteristics of the movement, to predict what will be those of the organ, 

 and vice versa. 



A long habit of comparing with each other the skeletons of different 

 animals enabled Ouvier to recognize among the difterent bones of an 

 animal certain relationships which he called the' subordination of 

 characters. A bone of a certain form implied the existence of certain 



La Machine Auimale, Chapter VIII. 



