146 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



However, in warm-blooded animals every operation in 

 the vicinity of the medulla oblongata is accompanied 

 by such severe shocks to the segmental respiratory 

 ganglia that the experimental proof is still wanting 

 for the ganglia of the medulla in higher Vertebrates. 

 It has been attempted with electrical stimuli, but 

 such experiments only show that some kind of proto- 

 plasmic connection exists between the stimulated spot 

 and the segmental ganglia of the active muscles. The 

 fact, for instance, that the respiratory movements are 

 affected by stimulation of the third ventricle only 

 proves that there are fibres at that place which go to 

 the segmental respiratory ganglia. The conclusion, 

 however, cannot legitimately be drawn from this that 

 respiratory ganglia or " respiratory centres" are located 

 in the third ventricle. Two facts have combined to 

 hinder the development of the segmental theory. 

 First, comparative physiology of the brain and embry- 

 ology have never been duly considered. Because the 

 brain of Vertebrates only reveals its segmental char- 

 acter in the earliest embryological condition, only a 

 small number of physiologists have thus far seriously 

 believed that the segmental character of the central 

 nervous system would furnish the key for comprehend- 

 ing its functions. The second fact is disregard of the 

 shock-effects upon those parts of the central nervous 

 system situated behind the seat of the operation. 

 It is possible that certain impulses flow constantly 

 from the cephalic to the lower parts of the central 

 nervous system. The stopping of these influences 



