ON THE FUNCTIONS OF THE CEREBRUM 297 



lamination. In the pref rental region of a foetus of six months it 

 is separated off from the rest of the cortex by the fourth or inner 

 fibre lamina, and is already within 29 per cent, of the normal 

 adult depth. In a child of six weeks it has advanced to within 

 18 per cent, of the normal adult depth. 



It is of extremely constant average adult depth. 



A very slight decrease in the depth of this layer exists in cases 

 of high-grade amentia and of chronic insanity with moderate 

 dementia. A considerable decrease, on the other hand, exists in 

 more marked aments (whether foetuses and infants, or idiots 

 and imbeciles), and in gross dements who are unable to carry on 

 the ordinary animal functions, such as attending to their own 

 wants, &c. 



The fifth, polymorphic, or inner cell lamina of the human cerebrum, 

 therefore, in association with the fourth or inner fibre layer, subserves 

 the lower voluntary and instinctive activities of the animal economy, 

 and thus forms a lower level basis for the carrying on of cerebral 

 junction. 



Final proof of the last statement has, from the phylogenetic 

 aspect, been afforded by the researches of Watson, who has shown 

 that the " infra-granular " region contains the important cell layers 

 of the lower mammalia, and is very little inferior in depth (see 

 Fig. 1, page 291) to the normal adult human depth of the conjoined 

 fourth and fifth laminse. 



Watson's conclusions on this question are as follows : 

 " The infra-granular portion of the cortex (iv. and v.) (omitting 

 the constituent cells which possess motor or analogous functions) is 

 concerned especially with the associations necessary for the perform- 

 ance of the instinctive activities, that is, all those which are innate 

 and require for their fulfilment no experience or education. These 

 form the basis of many complex actions necessary for the preservation 

 of the individual and the species, such as the seeking appropriate 

 shelter and protection, the hunting for food each after his own kind 

 and the quest of the opposite sex. Although these acts may be 

 accompanied by consciousness, there is no evidence to show that this 

 is ' focal ' or that essentially they are controlled by consciousness 

 (Lloyd Morgan). It is believed that lower mammals have provided in 

 the infra-granular cortex (which is relatively so fully matured at birth 

 in them as well as in man, and which in the adult, even in animals 

 low down in the mammalian scale, reaches such a great degree of 



