100 



PHYSIOLOGY OF FARM ANIMALS 



[CH. 



The thalamencejDhalon is the vesicle of the fore brain from 

 which the hemispheres arise in development as hollow outgrowths. 

 It comes to be completely obscured by the hemispheres. Here 

 all the afferent nerves of true sensation meet and then extend to 

 the hemispheres. 



The corpora quadrigemina or optic lobes are also almost 

 completely covered by the hemispheres. They contain centres 

 for the adjustment of the pupil of the eye for light, for sneezing, 

 and for various other movements. 



The cerebellum lies behind the hemispheres. Its surface is 



Fig. 48. Brain of dog (after Dalton, from Halliburton). 

 F frontal fissure; 1 — 9 motor areas (I and 2 for 

 head, 3 — 6 limbs, 7 — 9 facial muscles). 



folded, and it has grey matter outside and white matter within. 

 It is in reality a paired expansion of the pons, just as the cerebrum 

 is a paired expansion of the extreme anterior end of the central 

 nervous system. The cerebellum receives afferent nerves from 

 the semi-circular canals of the ear, and from many joints, muscles, 

 and tendons concerned with bodily movement. Nerve fibres 

 pass from this part of the brain to other parts of the central 

 nervous system and especially to the spinal cord. Injury to 



