Dissection of Sheep^s Brain. 171 



1st Section. To the Level of the Corpus Callosum. 

 The Hemisplieres should now be sliced off to a level with the 

 Corpus Callosum, when the white substance of that structure 

 will be seen connecting together both hemispheres, and 

 marked in the middle line by a longitudinal, central, ridge, or 

 raphe. The Student should here note the large expanse of 

 medullary matter* now exposed, surrounded by the convoluted 

 margin of grey substance. 



2nd Section. To Expose the Lateral Ventricles. 

 In order to see the thickness of the Corpus Callosum, and to 

 bring into view the parts in contact with its under surface, 

 a cut should be made through that body on each side near the 

 middle line, and continued parallel with it forwards and back- 

 wards as far as the limits of the underlying ' lateral ' ventri- 

 cles ; the rest of the Corpus Callosum, external to the above 

 longitudinal incisions on either side, which forms the roof of 

 the space within, should then be removed ; and inasmuch, as 

 a part of either ventricle extends down, in the middle lobe 

 towards the base of the Brain, the course of that cavity 

 should be followed by incisions along each side thereof ; and 

 the superjacent substance of the hemisphere should be re- 

 moved. The cavity passes at first backwards, outwards, and 

 downwards ; then curves around the Crus Cerebri, forwards 

 and inwards, nearly to the point of the * lobe of the Hippo- 

 campus,' close to the fissure of Sylvius. 



The two large irregular cavities exposed on removal of that 

 part of the Corpus Callosum, above described, are the Lateral 

 Ventricles, serous cavities separated by the vertical Septum 

 Lucidum ; each consists of a central cavity or body, and twof 

 smaller cavities or cornua ; of these the anterior cornu curves 

 forwards, outwards, and downwards in the substance of the 



* The centrum ovale majus of Vieussens. 



t Since the 'posterior' lobe of the Human Cerebrum is deficient in the Sheep, 

 the posterior cornu is also wanting. 



