Dissection of Sheep's Brain, 165 



Anteriorly there is the median longitudinal fissure between 

 the Cerebral hemispheres ; and, at some little distance within 

 the fissure, is the anterior border of the great transverse Cere- 

 bral commissure, called the Corpus Callosum. 



At the base of the anterior lobes of the hemispheres, are 

 situated the First Pair of Nerves, termed Olfactory , as being 

 the special nerves of the sense of smell : on reaching the 

 Cribriform plate of the Ethmoid bone they expand into a bulb 

 from which are given ofi" numerous filaments which pass 

 through the cribriform foramina and are distributed to the 

 mucous membrane of the nose. 



JSText may be noticed the Optic Commissure which rests upon 

 the Olivary process of the Sphenoid bone : the Optic Nerves 

 which proceed thence and are distributed exclusively to the eye 

 ball, have been cut away ; the optic tracts which remain pos- 

 terior to the commissure, and diverge laterally may be traced 

 back into the optic thalami and corpora quadrigemina. Just 

 within the angle of the optic tracts, immediately behind the 

 commissure, is the Tuber Cinereum : this forms part of the 

 floor of the third ventricle, and from it proceeds the Infundibu- 

 lum*, through which the cavity of the third ventricle above, 

 is continued into the remnant of the cavitj^ that existed in the 

 foetus in the Pituitary body below. 



Next, behind the Tuber Cinereum, is the Single f Corpus 

 Albicans, formed by the anterior Crura of the Fornix, which 

 after descending to the base of the brain are folded upon 

 themselves before passing upwards to the Thalami optici. 



The two cylindrical bundles of white matter which emerge 

 from the anterior border of the Pons, diverge as they pass 

 forwards, give origin from their inner margin to the 3rd pair 



* When the Brain is removed from the Skull, the Infundibulum is almost 

 ahvays cut through, leaving only a tubular orifice : and so also the Pituitary 

 body which was situated in the Sella Turcica of the Sphenoid bone. 



t In Man there are two Corpora Albicantia, except at an early period of foetal 

 life, when they are blended together in one large mass. 



