The Nervous System. 283 



forms the motor areas for certain groups of muscles on the 

 opposite side of the body. By irritating these areas con- 

 vulsions are produced, and by observation it is found 

 possible to distinguish areas for the eyelids, face, mouth, 

 tongue, tail, flexion and extension of the limbs, and many 

 others. For veterinary purposes, especially dealing as we 

 have done almost exclusively with herbivora, a knowledge 

 of these motor centres is not required, nor have the exact 

 positions of them been determined. We are content to 

 know of their existence, but to the human surgeon they 

 have opened up a new field of surgery, and one which 

 promises the most important results. 



After removal of the cerebral hemispheres all conscious- 

 ness is lost, but muscular movements and equilibrium are 

 retained. The cerebrum is insensitive to pain, but the 

 dura mater is highly sensitive. 



Besides the motor centres,, sensory centres in the brain 

 have been described, such as a visual, auditory, olfactory, 

 taste, and tactile centres. A heat centre has also been 

 described, stimulation of which produces a rise in tempera- 

 ture. The definite existence of these centres has not been 

 agreed upon. 



The respective functions of the grey and white matter 

 of" the cerebrum may be stated as follows : The grey 

 matter is the seat of intelligence and the higher faculties ; 

 to the cells of the grey matter run the sensory fibres, both 

 special and general ; from the grey matter proceed the 

 motor fibres supplying the voluntary muscles; the white 

 matter is simply the conducting area, whereby the im- 

 pressions made upon or issuing from the grey substance are 

 distributed. The fibres of the white matter are arranged 

 in a complicated manner, but ascending, descending, and 

 transverse fibres have been recognised. 



It has been supposed that the majority of the sensory 

 impressions are implanted on the posterior half of the 

 cerebrum ; while from the middle and lateral portions arise 

 the motor impulses; and from the anterior portion con- 

 sciousness and intelligence. 



