EXPERIMENTS ON VERTEBRATES 141 



ance of the coordination in movements first begins with 

 the apparent decrease in the ability to use the fore- 

 legs, which becomes more and more apparent the 

 nearer the incision approaches the origin of the bra- 

 chial plexus from the tip of the calamus scriptorius. 

 When this is reached the animal falls flat on its belly ; 

 the fore-legs are no longer able to carry the body. If 

 the animal be stimulated in the middle-line, for in- 

 stance at the anus, the hind-legs throw the body for- 

 ward. The forward extremities participate still with 

 4 alternating ' but insufficient and peculiar trembling 

 movements. A really coordinated progressive move- 

 ment no longer takes place." We see again in this 

 case the entire validity of the segmental theory : in- 

 juries of the spinal cord in the vicinity of the brachial 

 plexus interfere with the walking movements only in 

 so far as the cooperation of the fore-legs comes into 

 consideration. The hind-legs, on the other hand, 

 continue to function normally. Similar phenomena 

 may be observed in fishes. They also cease to move 

 about when the brain is removed up as far as the 

 medulla oblongata. It would be quite wrong, how- 

 ever, to conclude from this that the centre of locomo- 

 tion is located in the medulla oblongata. If the head 

 of a shark be amputated the body swims about spon- 

 taneously This experiment was made by Steiner. 

 From the standpoint of the segmental theory this re- 

 sult was to be expected. The tail is the organ of 

 locomotion for the shark, and only the corresponding 

 segmental ganglia of the spinal cord are required for 



