CEREBRUM 197 



A study of the development of the olfactory mechanism 

 throughout the mammalian series throws considerable light upon 

 the position of the cortical centre. Many mammals depend 

 very largely upon the sense of smell in their relationship with 

 the external, while others, e.g. man, use it less, and the cetacea 

 do not use it at all. In the first group, the osmatic mammals, 

 the olfactory bulbs and tracts are enormously developed (fig. 97). 



Each bulb terminates behind in three roots, the inmost 

 sending fibres across to the opposite side (fig. 51, IV.), the others 

 sending fibres to a part of the cortex at the base of brain just 

 outside the olfactory tracts (fig. 51, m.). In man and apes, from 

 the development of the temporo-sphenoidal lobe this region 

 gets carried outwards and is represented by a swelling, the lobus 

 pyriformis, on the inner aspect under the uncus (fig. 101). The 

 cortex in the region indicated in the figure has a peculiar 

 arrangement of cells. The medullated fibres to this area are 

 early developed (fig. 100A, 4a). 



Terrier states that removal of the hippocarnpal convolution, 

 including the lobus pyriformis in monkeys, leads to loss of taste 

 and smell, and that stimulation causes torsion of the nostrils 

 and lips, as if sensations of smell or taste were being 

 experienced. 



Touch. Ferrier thought that removal of the hippocampal 

 convolution caused loss of tactile sense, while Schafer describes 

 the gyrus fornicatus as the centre for this sense. It has 

 been objected that in removing this lobe the fibres going to 

 the areas on the outside of the cortex are apt to be injured. 

 According to the observations of Mott, when the cortex round 

 the fissure of Rolando in which the mechanism for causing 

 the various combinations of muscular movements is situated 

 is removed in the monkey, clips may be attached to the skin 

 on the opposite side of the body without attracting attention, 

 while if they are placed on the same side they are at once 

 removed. He therefore regards the Rolandic area of the brain 

 as connected with the reception of tactile impressions. 



This view is strongly supported by the evidence of morph- 

 ology. The ascending pariefcal convolution is early supplied 

 by medullated fibres coming from^the thalamus (fig. 100B 2), 

 and in it a type of cell distribution similar to that in the 

 other sensory areas exists (fig. 101). Further, in this region 



