FROG. 107 



Note the delicate pigmented membranes that 

 cover the brain and the spinal cord. The 

 outer, the dura mater, is often more or less 

 torn in removing the bone. The inner, the 

 pia mater, lies very close upon the nervous 

 tissue. It is usually more pigmented than 

 the dura mater. 



Before the brain can be removed for further 

 investigation it must be hardened by ex- 

 posure to formic aldehyde. 

 To remove the brain : 



Cut through the olfactory tracts (or nerves) close 

 to the nasal pits lift the anterior end of the 

 brain gently , cut through the cranial nerves 

 close to the skull and through the spinal 

 nerves. Take out the brain and spinal cord 

 and put into a small dish of water (or dilute 

 alcohol). 



Sketch the nervous system thus exposed : 

 1. The brain : the dorsal aspect (from before 

 backward) : 



(a) The olfactory lobes, each passing anteriorly 



into a cylindrical portion : the olfactory 

 tract. 



(b) The cerebral hemispheres, separated from 



each other by a deep cleft. They are 

 marked off from the olfactory lobes by 

 a slight transverse depression. 



(c) The thalamencephalon: immediately behind 



