320 NEKVOUS SYSTEM. 



confine our description, as far as possible, to anatomical facts 

 that have been definitively settled and are now generally ac- 

 cepted. But, as we have before remarked, the course of the 

 fibres and their connections are so exceedingly intricate, that 

 we cannot rely entirely upon purely anatomical investiga- 

 tions. The results obtained by anatomists should be con- 

 trolled, as far as possible, by physiological and pathological 

 observations. When anatomical researches are directly op- 

 posed to the conclusions to be deduced from experiments 

 upon living animals, in view of the great uncertainty of the 

 former, it will generally be reasonable to assume that they 

 are erroneous or incomplete. We know, as the results of 

 experiments on animals, that the motor stimulus is con- 

 ducted from the brain by the antero-lateral columns of the 

 cord, and that the conducting fibres decussate at the medulla 

 oblongata. This fact has been verified by pathological ob- 

 servations, chiefly in cases of injury to the brain-substance 

 from haemorrhage, softening, etc. We know that impres- 

 sions are appreciated as sensations in some part of the cere- 

 brum, and that the sensory conductors also decussate ; as is 

 shown by occasional paralysis of both motion and sensation 

 following brain-lesions. It is evident, therefore, that sensory 

 conductors pass to the brain, but their precise course is not 

 easy to determine. We have seen, in treating of the action 

 of the cord as a conductor, that sensory impressions are 

 transmitted by the gray substance alone, and it is probably 

 through connections between the cells of the different cen- 

 tres that these impressions are finally carried to the brain. 

 The physiological fact of the conduction of sensory impres- 

 sions is fully confirmed by pathology, but its mechanism has 

 been very little, if at all, elucidated by anatomical re- 

 searches. 



We have left certain anatomical points relating to the 

 cerebrum, cerebellum, tiiber annulare, and medulla oblon- 

 gata, to be described separately in connection with these 

 'divisions of the encephalon. 



