230 ELEMENTARY BIOLOGY. [XIII. 



each side, noting the small nerves running into it 

 on each side of the middle line ; remove the muscles 

 lying on the arches of the vertebra ; open the neural 

 canal by dividing the membrane between the atlas 

 and occiput; then introduce one blade of a small, but 

 strong, pair of scissors into the cranial cavity, and cut 

 away bit by bit the bones whicb form the roof of the 

 skull, taking care that the point of the scissors does 

 not injure the brain. Next remove the upper part 

 of the arches of the vertebrae in a similar manner. A 

 delicate pigmented membrane (the pia-mater) is now 

 laid bare, covering the brain ; over the spinal cord 

 it is usually concealed by a quantity of soft material ; 

 gently remove this with a pair of forceps or wash it 

 away with a syringe. 



2. The brain. 



On the dorsal aspect of the brain, which is now exposed, 

 the following parts will be seen ; 



a. In front, two elongated masses forming about the 

 anterior half of the brain: a slight transverse 

 depression divides each into an anterior smaller 

 and a posterior larger portion. The inner faces 

 of the anterior portions are closely united to- 

 gether; those of the posterior portions are sepa- 

 rated by a cleft. The posterior portions are the 

 cerebral hemispheres (prosencephalon) ; the an- 

 terior, the bases of the olfactory lobes (rhinence- 

 phalon). 



a. The olfactory lobes become narrowed into two 

 rounded trunks (commonly termed the olfactory 

 nerves), which leave the skull, and applying them- 

 selves to the outer face of the lining membrane of 



