94 ELEMENTS OF COMPARATIVE ZOOLOGY. 



In the brain make out, viewed from above, in front the 

 olfactory lobes; next the large cerebrum, and behind this 

 the cerebellum, and following the cerebellum the medulla 

 oblongata, broad in front and tapering behind into the 

 spinal cord. Are any of these parts paired ? The line 

 between medulla and spinal cord is not a sharp one, and the 

 place of passage through the skull may be regarded as the 

 boundary. Sketch these parts in outline from above and 

 from the side, X 2. 



Over the whole brain is a rather tough membrane, the 

 dura mater, which is next to be removed from the dorsal 

 surface. Do you find any convolutions on the cerebrum ? 

 Cut through the olfactory lobes as far forward as possible, 

 and lift the cerebrum very carefully from in front. It 

 will be found to be tied by the optic nerves, going from 

 the ventral surface. Cut these as close to the skull as pos- 

 sible. Do the olfactory lobes arise from the tip of the 

 cerebrum ? Roll the brain very carefully to the left side, 

 looking at the same time at the right side of the medulla 

 for nerves. From its anterior angle (below the cerebellum) 

 will be found a strong nerve, the trigeminus, and just 

 behind it another nerve, the facial and auditory com- 

 bined. Some distance farther back, yet still inside the 

 skull, arises a more complex nerve, consisting in reality 

 of three, the glossopharyngeal, the vagus, and the spinal 

 accessory. (Thus we can easily make out in the rat the 

 following nerves: I, olfactory; n, optic; v, trigeminal; 

 vn, facial; vin, auditory; ix, glossopharyngeal ; x, vagus 

 or pneumogastric ; xi, spinal accessory. The other nerves 

 are not easily made out on so small a form.) 



Tip the cerebrum forward, and notice between it and the 

 cerebellum the optic lobes behind and the 'twixt-brain in 

 front. How does this compare with what was found in the 



