252 VERTEBRATES. 



8. Two pairs, which arise, by many slender rootlets, 

 from the ventral surface of the hindmost part of the 

 brain, rootlets of one pair in part from the anterior end 

 of the spinal cord. 



Parts of the Brain. Cut off the spinal cord, and place 

 the brain in a little alcohol, for a superficial examination 

 of its parts. On the dorsal side, note the large, smooth, 

 cerebral hemispheres immediately behind the olfactory lobes, 

 and in the posterior angle between them, 011 the median 

 line, the pineal body. Posterior to the hemispheres, the 

 cerebellum covers the greater part of the dorsal surface. 

 It is made up of a large, transversely ridged, central lobe; 

 a pair of oblique, lateral lobes; and, on its outer edges, a 

 pair of small, rounded, floccular lobes. The dorsal sur- 

 face of the medulla appears behind the central lobe of the 

 cerebellum. 



On the ventral surface observe the olfactory lobes, 

 extending backward, beneath the anterior end of the 

 hemispheres. Observe that a large, oval, temporal lobe is 

 marked off on the ventral surface by a shallow groove 

 from the remainder of each hemisphere. Observe the 

 crossing of the optic nerves. They may be traced out- 

 ward and backward to the concealed optic lobes by turn- 

 ing the temporal lobes of the hemispheres aside. Close 

 behind the crossing of the optic nerves find a narrow 

 median slit, the aperture of the infundibulum, leading 

 down into the pituitary body, which was probably left be- 

 hind in the base of the cranium when the brain was 

 removed. The floccular and lateral lobes of the cerebel- 

 lum are visible on either side, and these are connected 

 across the ventral surface by a stout band of nerve fibers. 

 The medulla, tapering posteriorly, and studded with nu- 

 merous nerve roots, forms the remaining posterior part of 

 the ventral surface. 



