808 THE CENTRAL NERVOUS SYSTEM 



upon the lowering of arterial blood pressure which a section of the 

 cord higher than the mid-dorsal region must entail. The poor nutritive 

 condition of the skin which we have seen to exist in the hind limbs 

 in shock, shows that the blood vessels in them are profoundly dilated, 

 but evidently the fall in blood pressure has nothing to do with the 

 faulty conduction through the spinal cord, for such a fall would affect 

 the centers for the fore limbs as well as those for the hind, and yet 

 the former show no symptoms of shock. 



Exactly similar shock is obtained by any section of the spinal cord 

 as high up as the medulla. Of course as the section is made higher and 

 higher up, the resulting paralysis becomes more and more marked, and 

 may reach such a degree of severity that recovery of the animal be- 

 comes an impossiblity. 



When we come to consider the functions of the various parts of the 

 brain, we shall have occasion to study the effects following section at 

 higher levels of the cerebrospinal axis. Meanwhile, however, it is im- 

 portant to note that when a section is made across the crura cerebri, so 

 that the cerebral hemispheres alone are isolated from the rest of the 

 nervous system, a condition of contracture of all of the extensor muscles 

 occurs. This condition is known as decerebrate rigidity. 



