726 FUNCTIONS OF THE CEREBRUM [CH. L. 



and absolute value of any locality in the central nervous system 

 depends largely on the degree to which centralisation has progressed, 

 and on the amount of connection between the various areas. The 

 closer the connection, the more numerous and intricate the path- 

 ways, the greater will be the permanent effects of an extirpation, 

 and the recovery of function the more remote. The lower the 

 animal in the zoological series, or the less the age of the animal, the 

 more imperfectly developed will be the connecting strands, and so 

 the possibility of other parts taking up to some extent the functions 

 of those that are removed will be increased. 



The earliest to work in the direction of localisation were Hitzig 

 and Fritsch. The subject was then taken up by Terrier and Yeo, 

 and later by Schafer, Horsley, etc., in this country, and by Munk 

 and many others in Germany. 



The main point which these researches have brought out is 

 what we have just termed the overwhelming importance of the 

 cortex; it contains the highest cerebral centres. Before Hitzig 

 began his work, the corpus striatum was regarded as the great motor 

 centre, and the optic thalamus as the chief centre of sensation ; and 

 the idea that the basal ganglia were so important arose from the 

 examination of the brains of people who had died from, or at least 

 suffered from, cerebral haemorrhage. 



The most common situation for cerebral haemorrhage is either in 

 the region of the corpus striatum or optic thalamus ; it was noticed 

 that motor paralysis was the most marked symptom if the corpus 

 striatum was injured, and sensory paralysis if the optic thalamus 

 was injured. The paralysis, however, is due, not to injury of the 

 basal ganglia, but of the neighbouring internal capsule. The internal 

 capsule consists in front of the motor fibres passing down from the 

 cortex to the cord, and behind of the sensory fibres passing up from 

 the cord to the cortex (see p. 689). Hence, if these fibres are ploughed 

 up by the escaping blood, paralysis naturally is the result. If a 

 haemorrhage or injury is so limited as to affect the basal ganglia only, 

 and not the fibres that pass between them, the resulting paralysis is 

 slight or absent. 



The question will next be asked : What, then, is the function of 

 the basal ganglia ? They are what we may term subsidiary centres : 

 the corpus striatum, principally in connection with movement, and 

 the optic thalamus, in connection with sensation, including the sense 

 of vision, as its name indicates. 



A subsidiary centre may be compared to a subordinate official in 

 an army. The principal centre may be compared to the commander- 

 in-chief. This highest officer gives a general order for the movement 

 of a body of troops in a certain direction ; we may compare this to 

 the principal motor-centre of the cortex sending out an impulse for 



