FUNCTIONS OF TEE BRAIN. 41 



The different lines of proof which I have taken up 

 establish conclusively the proposition that all the motor 

 impulses ivMch have the cortex pass out, in healthy animals, 

 from the convolutions about the fissure of Bolaiiido. 



When, however, it comes to defining precisely what is 

 involved in a motor impulse leaAing the cortex, things grow 

 more obscure. Does the imjjulse start independently from 

 the convolutions in question, or does it start elsewhere and 

 merely flow through ? And to what particular phase of 

 psychic activity does the activity of these centres corre- 

 spond ? Opinions and authorities here divide ; but it will 

 be better, before entering into these deeper aspects of the 

 problem, to cast a glance at the facts which have been 

 made out concerning the relations of the cortex to sight, 

 hearing, and smell. 



Sight. 



Ferrier was the first in the field here. He found, when 

 the angular convolution (that lying between the ' intra 

 parietal ' and ' external occipital ' fissures, and bending 

 round the top of the fissure of Sylvius, in Fig. 6) was ex- 

 cited in the monkey, that movements of the eyes and head 

 as if for vision occurred ; and that when it was extirpated, 

 what he supposed to be total and permanent blindness 

 of the opposite eye folloAved. Munk almost immediately 

 declared total and permanent blindness to follow from de- 

 struction of the occipital lobe in monkeys as well as dogs, and 

 said that the angular gyrus had nothing to do with sight, 

 but was only the centre for tactile sensibility of the eyeball. 

 Munk's absolute tone about his observations and his theo- 

 retic arrogance have led to his ruin as an authority. But he 

 did two things of permanent value. He was the first to 

 distinguish in these vivisections between sensorial and 

 psychic blindness, and to describe the phenomenon of resti- 

 tution of the visual function after its first impairment by 

 an operation ; and the first to notice the hemiopic character 

 of the visual disturbances Avhich result when only one 

 hemisphere is injured. Sensorial blindness is absolute 

 insensibility to light ; psychic blindness is inability to rec- 

 ognize the meaning of the optical impressions, as when we 



