824 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



terminating in the cortex traverse the basal ganglia ; others, constituting 

 the so-called pyramidal tracts, proceed from the motor regions of the 

 cerebrum and pass through the white matter and converge in the internal 

 capsule, and from there enter the crura cerebri, thence to the pons, and 

 thence to the opposite side of the medulla oblongata. 



The white matter of the cerebral lobes may, therefore, be considered 

 merely as the continuation of the paths of conduction of the cord and 

 medulla which terminate in the cells of the gray matter of the convolutions. 



The consideration of the cerebral lobes resolves itself, therefore, into 

 the study of the functions of the gray matter of the cortex. While the 

 cerebrum has been from time immemorial looked upon as the seat of the 

 will and intelligence, and, in fact, of all the psychical functions, it is only 

 since 1810 that attempts to localize the different functions of the cortex 

 have been attended by any measurable success. 



In the lower animals, when the cerebral hemispheres are removed 

 slice by slice, the animals simply become more and more dull and stupid, 

 until finally they lose all intelligence. When in pigeons both cerebral 

 hemispheres are removed the animals apparently appreciate no pain 

 during the operation, nor are any movements produced by operations on 

 the cerebral substance. After extirpation of the cerebral lobes they 

 pass into a semi-comatose or stupid condition, and, if not disturbed, 

 remain absolutely motionless, apparently experiencing no sensation of 

 hunger, and will die of starvation in the midst of food without making 

 any effort to feed. If mechanically disturbed, provided the basal ganglia 

 are intact, they are capable of moving in a perfectly normal manner, 

 will, to a certain extent, avoid obstacles, the pupils of their eyes react 

 to light, and they are capable of reacting to A'iolent sudden noises. If 

 food is placed in their mouths they are capable of swallowing it, and, 

 in fact, they preserve the power of completing numerous co-ordinated 

 movements which depend upon reflex stimuli, indicating that the 

 mechanisms concerned in the maintenance of equilibrium are located in 

 the mid-brain, probably in the corpora quadrigemina. 



If a single cerebral lobe is removed in the lower animals no effect 

 other than the apparent dulling of intelligence is evident. In the higher 

 animals after such a mutilation there is evident a certain dulling of 

 sensibility and difficulty in movement on the opposite side of the body, 

 which, however, finally in the majority of cases gradually disappear. It 

 is concluded from these experiments that the cortex is the chief if not 

 the exclusive seat of intelligence. 



From the experiments of Fritsch and Hitzig in 1870 dates a new 

 era in our knowledge of the functions of the cerebral cortex. They 

 found that stimulation by means of electricity of certain circumscribed 

 regions on the surface of the cerebral convolutions was followed by 



