364 THE NERVE SYSTEM 



portions with the same half of the cerebrum; (2) 

 commissural fibers which pass between the two 

 halves of the cerebrum and connect similar areas 

 w r ithin each; they cross in the middle line of the 

 brain and form commissures; (3) projecting fibers, 

 which connect the cerebrum with lower nerve centres 

 in the brain and spinal cord, and other fibers that 

 connect the lower centres with the brain. 



The Weight of the Brain. The average weight of 

 the human brain in the adult male is 1400 grams 

 (49.5 ounces); in the female, 1250 grams (44 ounces); 

 in the newborn, 400 grams (14.1 ounces). 



THE FUNCTIONS OF THE CEREBRUM. The functions 

 of the cerebrum have been discovered as a result of 

 a study of the anatomic development of the brain, 

 and examination of brains of various animals, human 

 beings, etc., and a study of diseases or injured brains, 

 certain parts of which have been rendered inactive 

 by the destruction of nerve cells and their processes; 

 such a destruction of tissue has been manifested in 

 different parts of the body by an interference or loss 

 of the function of the extremity, etc., to which the 

 nerve leading from or to the diseased region in the 

 brain is distributed. Thus it has been determined 

 that certain areas of the brain contain nerve cells 

 and nerve fibers which control definite functions of 

 the body, and are grouped into definite areas, irregu- 

 larly marked off by fissures, and correspond to the 

 convolutions seen on the surface of the cerebrum. 

 These areas are spoken of as the cortical localization 

 of function. 



Cortical Localization of Function} Motor Area. 

 Comprises the precentral gyre and parts of the frontal 

 gyres adjacent thereto, together with the paracentral, 

 and the adjacent portion of the superfrontal gyre on 

 its inner aspect. This area comprises the centres for 



1 See Figs. 129 and 130, page 365. 



