254 Mr. Victor llorsl'n [Marcli 27, 



describe. These white fibres coming away from it to the cord, not 

 only are channels convoying messages down to the muscles, but also 

 carrying messages from the innumerable sense corpuscles all over the 

 body. 



So much for one grey mass of centres. Now down here at the base 

 of the brain you see two lumps or masses of the same nature, and 

 these are called therefore the basal ganglia or grey masses. Since they 

 are placed at the side of the paths from the cortex, and undoubtedly 

 do not interfere with the passage of impulses along those paths, we 

 may put them aside, remembering that they i)robably are concerned 

 with low^ actions of the nervous system, such as eating, &c., which are 

 pojmlarly termed automatic functions. 



In this photograph of a model made by Professor Aeby, of Berne, 

 you see represented from the front the two cerebral hemisj^heres with 

 the centres in the cortex as little masses on the surface, and the basal 

 ganglia as darker ones at the bottom, while leading from them down 

 into the spinal cord are wires to indicate the channels of commu- 

 nication. 



Note in passing that both hemispheres are connected by a thick 

 band of fibres called the corpus callosum. It is, I believe, the close 

 union thus produced between the two halves that leads in a great 

 measure (though not wholly) to consonance of ideas. 



The arrangement of the fibres will be rendered still clearer by this 

 sclieme, in which the cortex is represented by this concave mass, and 

 the fibres issuing from the same by these threads. 



The basal ganglia would occupy this position, and they have their 

 own system of fibres. 



I will now leave these generalisations, and ex[)lain at once the 

 great advance in our knowledge of the brain that has been made 

 during the last decade. The remarkable discovery that the cortex or 

 surface of the brain contained centres which governed definite groups 

 of muscles, was first made by the German observers Hitzig and 

 Fritsch ; their results were, however, very incomplete, and it was 

 reserved for Professor Ferrier to produce a masterly demonstration of 

 the existence and exact position of these centres, and to found an 

 entirely new sclieme of cerebral physiology. 



The cortex of the brain, although it is convoluted in this exceed- 

 ingly complex manner, fortunately show^s great constancy in the 

 arrangement of its convolutions, and we may therefore readily grasp 

 the main features of the same without much trouble. 



From this photograph of the left side of an adult human brain, 

 you will see that its outer surface or cortex is deeply fissured by a 

 groove running backward just below its middle, which groove is 

 called the fissure of Sylvius, after a distinguished med:a)val anatomist. 

 This fissure if carried upwards would almost divide the brain into a 

 motor half in front and a sensory half behind. 



Of equal practical importance is another deep fissure which runs 

 at an open angle to the last, and which is called the fissure of Kolando, 



