THE BRAIN. 



507 



the fibers of the posterior commissure connect the optic thalami, 

 while some come from the tegmentum of one side, traverse the 

 optic thalamus, and terminate in the white matter of the temporo- 

 sphenoidal lobe of the other side. 



3. The third group, association fibers, connect different struct- 

 ures in the same hemisphere ; as the short association fibers, which 

 connect adjacent convolutions, and the long association fibers, which 

 connect more distant parts. 



Functions of the Cerebrum. That the cerebrum is not essential 

 to life has been demonstrated experimentally many times in birds, 

 fishes, rats, and other animals. Of course, the same kind of proof 

 is not available in man, but there are instances on record in which 



FIG. 298. Dr. Harlow's case of recovery after the passage of an iron bar through 



the head. 



the destruction of cerebral tissue has been so great as to warrant the 

 statement that in man, as well as in lower animals, life may be 

 maintained without the influence of the cerebrum. A remark- 

 able instance is that of a man who was injured by a premature 

 blast, an iron bar, one inch in diameter, being driven through the 

 skull and brain. Although delirious and unconscious for several 

 weeks, he finally recovered, with but the loss of one eye. He 

 lived more than twenty years after the injury, and performed the 

 work of a coachman and a farm-laborer. 



The cerebrum is undoubtedly the seat of the intellectual 

 faculties. A study of the lower animals reveals the fact that 

 according as the hemispheres are developed the signs of intelli- 

 gence are increased : when these structures are destroyed there is 

 an absence of these manifestations. 



When the hemispheres are removed, spontaneous action ceases. 

 In studying the reflex action of the spinal cord in a decapi- 

 tated frog it was seen that the animal made no attempt to move 



