82 DISSECTION OF THE BRAIN. 



Remove carefidly with forceps and knife the corpus 

 callostim itntil the lateral ventricles are exposed, taki7tg' 

 care not to injure the fornix, ivhich lies immediately 

 beneath. 



c. The Lateral Ventricles, one on each side,, 

 fully exposed after complete removal of the corpus 

 callosum. In each three chambers or horns may be 

 distinguished ; the anterior cormt, a narrow slit run- 

 ning forward and separated from the anterior cornu 

 of the other side by a vertical partition — the septun-i 

 lucidum ; the descending cornu, situated posteriorly 

 and curving downward and outward ; the posterior 

 cornu, situated at the most posterior end of the ven- 

 tricle, a small diverticulum running backward, very 

 inconspicuous in the dog. 



d. The Septum Lucidum is the vertical partition 

 lying between the anterior cornua of the two ventricles. 

 It contains within its walls a small cavity, the so- 

 called 5th ventricle, not formed by the closing in of 

 the embryonic medullary tube like the other true 

 ventricles of the brain. 



e. The Corpus Striatum is the oval mass pro- 

 jecting into each anterior cornu from the side of the 

 cerebral hemisphere. Only a part of the corpus 

 striatum is seen in the dissection ; the remainder is 

 concealed in the walls of the hemisphere. It is 

 originally an outgrowth from the floor of the vesicle 

 of the cerebral hemispheres, and contains two nuclei of 

 gray matter in its interior — the micleus ca^idatiis, con- 

 tained within the part which projects into the ven- 

 tricle, and the nucleiis lenticularis, contained within 

 the part buried in the ,wall of the hemisphere. 



Lay open the descending cornu on one side by care- 

 fully cutting away the sides of the cerebral hemisphere. 



