24 



ANIMAL LOCOMOTION. 



animals to apply their travelling surfaces to the media on 

 which they are destined to operate at any degree of obliquity 

 so as to obtain a maximum of support or propulsion with a 

 minimum of slip. If the travelling surfaces of animals did 

 not form screws structurally aud functionally, they could 

 neither seize nor let go the fulcra on which they act with the 

 requisite rapidity to secure speed, particularly in water and air. 



Ligaments, — The office of the ligaments with respect, to 

 locomotion, is to restrict the degree of flexion, extension, and 

 other motions of the limbs within definite limits. 



Effect of Atmospheric pressure on Limbs. — The influence of 

 atmospheric pressure in supporting the limbs was first noticed 

 by Dr. Arnott, though it has been erroneously ascribed by 

 Professor Miiller to Weber. Subsequent experiments made 

 by Dr. Todd, Mr. Wormald, and others, have fully established 

 the mechanical influence of the air in keeping the mechanism 

 of the joints together. The amount of atmospheric pressure 

 on any joint depends upon the area or surface presented to 

 its influence, and the height of the barometer. According to 

 Weber, the atmospheric pressure on the hip -joint of a man 

 is about 26 lbs. The pressure on the knee-joint is estimated 

 by Dr. Arnott at 60 Ibs."^ 



Active organs of Locomotion. Muscles, their Properties, Ar- 

 rangement, Mode of Action, etc. — If time and space had per- 

 mitted, I would have considered it my duty to describe, more 

 or less fully, the muscular arrangements of all the animals 

 whose movements I propose to analyse. This is the more 

 desirable, as the movements exhibited by animals of the 

 higher types are directly referable to changes occurring in 

 their muscular system. As, however, I could not hope to 

 overtake this task within the limits prescribed for the present 

 work, I shall content myself by merely stating the properties 

 of muscles ; the manner in which muscles act ; and the man- 

 ner in which they are grouped, with a view to moving the 

 osseous levers which constitute the bony framework or skele- 

 ton of the animals to be considered. Hitherto, and by 

 common consent, it has been believed that whereas a flexor 

 muscle is situated on one aspect of a limb, and its correspond- 

 1 Bishop, op» cit. 



