62 LABORATORY WORK. 



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 ct>m- 

 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; 

 vii, facial; vm, auditory; ix, glossopharyngeal; x, vagus 

 or pneumogastric ; xi, spinal accessory. The other nerves 

 are not easily seen 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 

 dogfish? Tip the cerebellum forward and see the large 

 triangular opening in the roof of the medulla. 



On the lower surface of the brain see the cut optic 

 nerves. From which division of the brain do they arise? 

 Behind the optic nerve find a median lobe, the hypophysis 

 or pituitary body. 



With a sharp scalpel make a series of cross-sections 

 through the cerebrum. Are the two halves completely 

 separate? In each half find a cavity (ventricle), and above 

 it in the solid tissue a transverse lighter band (corpus 

 callosuni). Draw the section. Make similar sections 

 through the 'twixt-brain and the optic lobes. How many 

 cavities do you find here? Draw each section. 



Cut a longitudinal vertical section through the cerebel- 

 lum to left of median line, and notice the way in which the 

 cerebellum is folded. The somewhat bush-like structure is 



