THE NERVOUS SYSTEM 



2I 9 



Experiment 65. To show the brain. Get a sheep's brain from the 

 butcher. Pay him to dissect away the skin and muscles of the skull, 

 under your direc- 

 tion, and to saw 

 open the cranium in 

 such a manner as 

 to expose the entire 

 upper surface of the 

 brain. Remove the 

 sawed top and care- 

 fully tear off the 

 dura mater from 

 the bones. 



Now cut away 

 enough of this mem- 

 brane so that the 

 sides of the skull 

 can be sawed and 

 torn away, to allow 

 the brain to be lifted 

 out in fair condition. 

 Put all the torn parts 

 and membranes 

 back into place. 



The sheep's 

 brain is very small 

 and not to be com- 

 pared in size with 

 that of a man, but 

 the general arrange- 

 ment of the parts is 

 the same. 



Note the dura mater, the tough, outer membrane ; the arachnoid, 

 the thin membrane which lines the dura mater ; and the pia mater, the 

 delicate membrane which is closely attached to the brain. Find the 

 cerebrum, or big brain ; the cerebellum, or little brain ; the medulla, 

 and the stumps of the cranial nerves (Note, p. 218). 



In the cerebellum examine the curious folded arrangement of the 

 gray and white matter forming the arbor vitae. Cut open the cerebral 



FIG. 137. The Base of the Brain. 



A, anterior lobe of the cerebrum ; B, olfactory nerve ; 

 C, portion of the posterior lobe ; >, optic chiasm ; 

 E, optic tract ; //, M, hemispheres of the cerebellum ; 

 K, portion of the occipital lobe ; N, medulla oblongata ; 

 R, pons Varolii. (See also Fig. 98.) 



