DISSECTION OF THE BRAIN. 275 



). Dissection of the Brain. 



1. Removal of the brain. 



Cut across the medulla a short way behind the roots of the 

 'agus. Cut through the olfactory nerves so as to separate the 

 ^factory lobes from the nasal capsules ; and cut through the 

 everal cranial nerves one by one, about midway between the 

 train and the skull-wall. Turn out the brain fro^n the cranium, 

 aking care not to damage the pituitary body : this latter lies 

 m the under surface of the brain, opposite to the optic lobes, 

 md in a hollow of the skull-floor, to ivhich it 'is firmly 

 ittached, and from which it must be dissected away. 



Examine the skull after removal of the brain, and identify 

 )he several nerve-stumps and their foramina of exit. 



2. The ventral surface of the brain. 



Place the brain in spirit, with the ventral surface upwards, 

 md identify the following structures. 



a. The prosencephalon is marked by a shallow median 



groove ; posteriorly it is directly continuous with 

 the thalamencephalon. 



b. The olfactory lobes have much the same appearance 



as from the dorsal surface. 



c. The optic chiasma is formed by the decussation of 



the optic nerves on the under surface of the 

 thalamencephalon. Beyond the chiasma the 

 nerves diverge outwards towards the foramina 

 in the skull- wall which lead to the orbits. 



d. The infundibulum consists of a pair of prominent 



oval swellings, sometimes called lobi inferiores, 

 on the under surface of the thalamencephalon, 

 immediately behind the optic chiasma. 



e. The pituitary body is a thin-walled sac immedi- 



ately behind the infundibulum, and attached to 

 it. It is produced laterally into two thin-walled 

 pouches, the sacci vaseulosi; and it has along 

 its ventral surface a median tubular body of 



