PHYSIOLOGY OF THE CRANIAL NEEVES. 433 



been supposed to effect a connection between the two hemi- 

 spheres in the more complex mental actions. It should be 

 remarked, however, that cases are known of absence or de- 

 struction of one hemisphere, in which all the more common 

 acts of the mind seemed to be quite normally carried on. 



The fornix and commissures of the optic thalami and 

 corpora striata are supposed to connect those organs on the 

 two sides between which they are placed, so that the action 

 on the two sides may be uniform ; but their true function 

 has been by no means satisfactorily ascertained. The func- 

 tions of the pineal and pituitary bodies are equally involved 

 in mystery. 



The nerves originating from the encephalon are 24 in 

 number, and arranged in pairs, which are named first, 

 second, third, &c., counting from before backward. They 

 also receive special names, according to their functions, or 

 the parts to which they are distributed. They may be 

 classified according to their functions ; thus, 1st, Nerves of 

 special sense olfactory, optic, auditory, part of the glosso- 

 pharyngeal, and the lingual branch of the fifth. 2d, Nerves 

 #f common sensation the greater part of the fifth, and a 

 portion of the glosso-pharyngeal. 3d, Nerves of motion 

 third, fourth, smaller division of the fifth, sixth, seventh, 

 and twelfth. 4th, Mixed nerves pneumogastric and spinal 

 accessory. 



The first pair, or olfactory nerves, arise from the olfactory 

 lobes, two prolongations of grey, matter from the anterior 

 part of the cerebrum, and of very large size, in the domestic 

 animals. The nerves pass, as numerous filaments, through 

 two perforated bony plates, to ramify in the mucous mem- 

 brane in the depth of the nasal chambers. It is acknow- 

 ledged on all hands that these nerves preside over the 

 special sense of smell, and accordingly we find them largely 



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