DISSECTION OF THE BRAIN. 283 



D. Dissection of the Brain. 



1. Removal of the brain. 



Gut across the medulla a short way behind the roots of 

 the vagus. Cut through the olfactory nerves so as to separate 

 the olfactory lobes from the nasal capsules ; and cut through the 

 several cranial nerves one by one, about midway between the 

 brain and the skull-wall. Turn out the brain from the cranium, 

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

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

 and in a hollow of the skull-floor, to which it is firmly attached, 

 and from which it must be dissected away. 



Examine the skull after removal of the brain, and identify 

 the 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, 

 and 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. It is 

 produced posteriorly into a large thin-walled 

 pouch, the saccus vasculosus. 



e. The pituitary body is a thick-walled median tubular 

 body lying immediately beneath and attached to 

 the infundibulum, the posterior end being, in the 



