LOCOMOTION IN BATRACHOSEPS. 283 



action which in turn throws the body forward. The shock pro- 

 duced by the sudden halt of muscular action causes flexion of 

 the limb which has just reached the limit of extension, and the 

 pulling of the skin at the inguinal region by this same extension, 

 starts up extensor movements in the opposite limb, which in its 

 turn coming in contact with the ground goes through the same 

 cycle of movements just completed in its fellow. And so on, the 

 action of one leg determines that of the other, so that not only 

 walking but running movements in the hind-legs may be, and 

 probably are, kept up indefinitely, involving the use of no more 

 of the nerve-cord than that part in which these simple sensory- 

 motor impulses may be exchanged. 



According to Phillipson's analysis it appears quite possible 

 that, after progressive locomotion has once been started in a normal 

 dog, it i/iight walk or even run a distance vvitJwut any additional 

 impulses passing down from the npper region of the spinal cord. 



3. The question now arises, could normal walking movements 

 in tJie liind legs of an animal be initiated without any impulses 

 whatsoever, for the purpose, coming into the lumbar centers from 

 levels of the cord higher, say, than the mid-dorsal region, or frcm 

 levels higher tlian the lumbar region itself. 



Loeb 1 has already suggested that the pendulum movements 

 in the hind-legs of a dog with severed nerve-cord may be caused 

 by the stretching of the skin on the sides of the body produced 

 by holding up the front part of the animal. He further held the 

 opinion that if the beast could stand at all on its legs it probably 

 could go through the coordinate movements necessary for walk- 

 ing. For, if the fore-legs took forward steps that action would 

 produce a pull on the sides of the body, stretching the skin. 

 This stretching would create sensory stimuli that would pass 

 into the lumbar region of the cord whence extensor motor stimuli 

 would pass into one leg or the other and thus start up the cycle 

 of ambulatory motions described by Phillipson. This view of the 

 possibility of coordinating anterior and posterior locomotion in a 

 vertebrate with severed nerve-cord receives strong support from 

 the experiments and observations of Friedlander. But it may be 



1 Loeb, Jacques, " Beitrage zur Gehirnphysiologie der Wiirmer. " Arch. f. d. ges. 

 Physiologic, 1894, 56, s. 268. 



