164 



VETERINARY PHYSIOLOGY 



2. THE VISUAL CENTRE IN THE CORTEX CEREBRI. 



A7i extensive lesion of one — say the right — occipital lobe, 

 (fig. 82), is accompanied by no loss of muscular power 

 but by bhndness for all objects in the opposite side of the 

 field of vision — i.e. the right side of each retina is blind. 

 The central spot of neither eye is completely blinded, because 



.^-\ 



FRONTAL 



MOTOR 



SENSORY- 



ECroSYLViANflf 

 eCTOSYLVIAN. B.. 



PARIETAL 



VISUAL 



Rkinica. 



S OrVLtiUi. 



. -S CruciattLS. 



--•S.Corona,lis- 

 H omologue 

 oj Rolanio 



■5Su,|)ra,si|lvi!u-S 



S Lateralis. 



S fctolaleralis. 



Caltirine 

 Post-calcarttve 



S PosUiteviUj. 



TueeRCULLiM OLFACl 



OLFACTORY. A.. 



OLFACTORY B 



rXTRA-RHINie. 



Fig. 82. — Superior and inferior aspects of the brain of the dog to show the various 

 sulci and the distribution of the chief receiving and reacting mechanisms. 

 Sensory is body sensibility. 



the fibres from the macula lutea only partially decussate at 

 the chiasma. 



Stimulation in this region in the monkey causes move- 

 ment of the eyes to the opposite side, as if some object were 

 perceived there. But destruction of the area does not 

 paralyse the movements of the eyes. 



In man, and the higher apes, the cortex in this region 

 shows a definite arrangement of cells, and a well-defined 

 band of white fibres in the middle of the layer of 

 granules (p. 183), which is thus duplicated (fig. 92). 

 This is the band of Gennari. In long-standing cases of 

 blindness the thickness of the layer of Gennari may be 

 reduced by 50 per cent., and of the outer layer of granules 

 by 10 per cent. 



The special characters of this area become more and more 



