i8o 



ELEMENTARY PHYSIOLOGY 



mother), which is very tough and fibrous. Its outer surface is 

 rough, and in contact with the inner surface of the skull, while the 

 inner surface is smooth, and is opposed to the outer surface of the 

 arachnoid. 



The brain consists of several parts, the chief of which are : 



1. The cerebrum or greater brain, which fills all the upper 

 and frontal portion of the cranium, and weighs about nine-tenths 

 as much as the entire brain. 



2. The cerebellum or lesser brain, which lies underneath the 

 back portion of the cerebrum. 



3. The pons Varolii (Lat. pans, a bridge), a broad band or 

 bridge of nerve matter which connects the right and left portions 



of the cerebellum, passing 

 round the medulla. 



4. The medulla oblon- 

 gata (Lat. oblong marrow), 

 which connects the brain 

 with the spinal cord. 



If we make a section of 

 the brain, we may observe 

 the arrangement of the 

 white and grey nervous 

 matter composing it. In 

 the cerebrum and cere- 

 bellum we find the grey 

 matter surrounding the 

 white matter, while in the 

 medulla oblongata the ar- 

 rangement is reversed. 



The student, remembering 

 the soft semi-solid condition of 

 the brains of an animal, may be 

 Fig. 165. Section through the Cerebral at a loss to know how a section 

 Hemispheres, showing the arrangement of the organ is to be made ; 

 of the White and Grey Matter. therefore we give the following 



simple and easy method by 



which the brain may be hardened and afterwards cut for examination : Place 

 the complete but skinned head of a rabbit or other animal into a jar of 

 methylated spirit, and let it remain in this for a few weeks. At the end of this 

 time dissect away all the flesh, leaving the skull clean, at least on the whole 

 upper surface. Now, with a small fret-saw, cut gently just through the skull 

 in several directions, and remove the bone, piece by piece, till the brain has 

 been entirely exposed. If the brain seems still too soft to handle, let it soak 

 in the spirit a little longer. It will be noticed that several nerves pass from the 

 under surface of the brain through openings in the bones, and it will be well 

 to preserve the origins of these nerves attached to the brain as far as possible. 



The cerebrum consists of two large hemispheres, the right and 



