300 THE EVOLUTION OF ANIMAL BEHAVIOUR 
save the segments to which the nerves for the arms proceed. 
“ Similarly,” writes Dr. Sherrington,* “in the cat and monkey, 
the reflex wagging of the tail persists when behind the spinal 
transection only the sacral region of the cord is left intact.” 
When the spinal cord of the dog is severed, so as to isolate 
that portion which is concerned with movements of the hinder 
part of the body, pressure on the pad of one hind-foot usually 
produces, not only a lifting of that leg, but also an extension 
of its fellow—that is to say, a co-ordinated response of the two 
limbs. But in the case of the vertebrates, more than in that 
of the invertebrates, the co-ordinated response of an isolated 
part of the central nervous system seems to lack the furtherance 
of its action, which normally comes from the higher centres 
from which it has been severed. ‘The spinal reflexes signifi- 
cant of progression seem,” says Dr. Sherrington,t “to con- 
tribute chiefly towards preparatory posture in readiness for the 
onset of action executed by the musculature under the driving 
of higher centres. Thus the well-known reflex spinal posture 
of the frog is flexion of the hind limbs, the extensors of the 
joints being taut and ready for the jump. ‘The spinal reflexes, 
which in their results approximate most closely to the normal 
reactions of the unmutilated individual, are those connected 
with the pelvic and abdominal viscera,” many of which “are 
executed as spinal reflexes in a manner presenting little or no 
physiological defect from the normal. And if the bulb ”—the 
continuation of the spinal cord within the skull to form the 
basal portion of the brain—“ be included with the spinal cord, 
and these together, including their nerves, be isolated from the 
rest of the nervous system, the animal as regards its visceral 
life, including that of the heart and lungs, is practically intact.” 
Huxley graphically describes the actions of a frog from 
which the cerebral hemispheres have been removed. “If that 
operation,” he says,{ “‘is performed quickly and skilfully, the 
* «The Spinal Animal,” p. 5. 
t Op. ctt., p. 28. 
$ “Collected Essays,” vol. i, essay on ‘ Animal Automatisin,” p. 
224, 
