DISSECTION OF THE BRAIN 249 



hinder end of the skull to expose the nerve in this part of its 

 course. Lay open the anterior cardinal sinus by slitting up 

 its dorsal wall ; wash out the contained blood, and identify 

 the branches of the vagus running along its inner wall and 

 across its floor. Dissect these branches out, and follow them 

 to their distribution. 



D. Dissection of the Brain. 



1. Bemoval of the brain. 



Cut 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. Tv/rn out the bradn 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 iden- 

 tify the several nerve-stumps and their foramina of exit. 



2. The ventral surface of the brain. {Cf. p. 240.) 



Place the brain inspirit, 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 crossing of the 



optic nerves on the under surface of the thalam- 

 encephalon. Beyond the chiasma the nerves 

 diverge outwards towards the foramina in the 

 skull-waU which lead to the orbits. 



d. The infnndibulum consists of a pair of prominent 



oval swellings, sometimes called lobi inferiores, 

 on the under surface of the thalamencephalon, 

 immediately behind the optic chiasma. 



