FUNCTIONS OF THE BRAIN. 



49 



printed letters of the alphabet, or words, signify certain 

 sounds and certain articulatory movements. If the con- 

 nection between the articulating or auditory centres, on the 

 one hand, and the visual centres on the other, be ruptured, 



L T. r. R.N.F 



L.0.5 



Fig. 15.— Scheme of the mechanism of vision, after Segiiin. The cuneus convolution 

 {Cu) of the right occipital lobe is supposed to Ite injured, and all the parts which 

 lead to it are darkly shaded to show that they fail to exert their function. F. O. are 

 the intra-hemispheric optical fibres. P. O. C. is the region of the lower optic cen- 

 tres (corpora geniculata and quadrigeinina). T. O. D. is the right optic tract; C, the 

 chiasma; F. L. D. are the fibres going to the lateral or temporal half T of the right 

 retina; and F. C. S. are those going to the central or nasal half of the left retina. 

 O. D. is the right, and O S. the left eyeball. The rightward half of each is there- 

 fore blind: in other words, the right nasal field, R. N. F., and the left temporal field, 

 L. T. F., have become invisible to the subject with the lesion at Cm. 



we ought a priori to expect that the sight of words would 

 fail to awaken the idea of their sound, or the movement for 

 pronouncing them. We ought, in short, to have alexia, or 

 inability to read : and this is just what we do have in many 



