The sensation goes by one set of tubes, and the messages to the fibres of the muscles come by another set.

11. In the body and in the limbs the two kinds of tubes are bound together in the same nerves. But in the face the two kinds of tubes are in two separate sets of nerves. There we have nerves of sensation and nerves of motion separate from each other, while everywhere else they are mingled together. But where they are thus mingled, they are just as separate in their office as where they are in separate

nerves.

12. Here, in Fig. 36, is a representation of the brain and spinal marrow, with the nerves branching out from them in all directions. At a is the cerebrum, the upper large brain filling up a large part of the skull, and at b is the cerebellum, the smaller brain lying underneath the cerebrum. You see the spinal marrow extending from the brain down the back. It is very much like the brain in its structure, and should really be considered as an extension of the brain itself. You see that nerves branch out from the brain and the spinal marrow all over the body.

13. You observe that the whole of this nervous system has two exactly similar halves, just as it is with the system of bones, and the system of muscles. The cerebrum has two parts just alike, called the two hemispheres of the brain. So it is with the cerebellum. There are two sets of nerves also for each half of the body that are just alike.

In what parts of the body are these tubes mingled together in the same nerves? Where are they in separate nerves? Describe the arrangement of the nervous system represented in Fig. 36. Is the nervous system single! What are the hemispheres of the brain?

14. In Fig. 37, you see the general arrangement of the brain. It is a view of one of the halves or hemispheres of the brain. It is the inside of the hemisphere that you see. At a b and c is the cerebrum; at ƒ is represented the white substance that joins this hemisphere to the other; at d is the cerebellum,

showing a very beautiful arrangement, called the arbor vitæ, or tree of life; at e is the beginning of the spinal marrow; at g is the beginning of the nerve of sight, and at 7 is the nerve of smell. Then there are various other nerves, which go to the eye and other parts of the face.

87.

15. You observe that the surface of the brain is very irregular. The brain does not touch the inside of the skull, but it is covered by three different membranes, one of which is very strong and thick, so as to protect this delicate organ from injury.

16. The brain is soft, something like blancmange. It is the softest organ in the body. It is composed of two kinds of substance. These are quite well represented in Fig. 38. Here the upper half of the brain is cut off, and you see the upper cut surface of the

What is said of the surface of the brain, and of its coverings? What is the consistence of the brain?

lower half. The outer shaded part is a grayish substance. All on the inside of this is a white substance. You see the dividing line between the two halves or hemispheres. In the middle of the Figure is represented a substance which makes a connection between the hemispheres. It is probably by means of this connection that the two halves of the brain act together as one brain.

17. It is curious to observe that the white part of the brain is just like the nerves. It is, like them, composed of very fine tubes. It is indeed a great central collection of the beginnings of nerves that branch out all over the body.

18. The outer gray part of the brain is, on the other hand, made up of cells, instead of tubes. This is supposed to be the working part of the brain.

The mind

acts directly upon the gray part when it moves any of the body. Thus, when you will to have your hand move, the mind does something, but what we know not, to some part of this gray substance. Then an impression or message is sent through those tubes in the white substance which are connected with this part of the gray substance. And as these tubes extend from the brain in the nerves to the muscles of the hand, the hand is moved.

19. In sensation all this is reversed. The impression travels just the contrary way. It goes to the brain, and not from it, as it does in motion. If any one touches you, the impression is carried by the nervous

What are the two kinds of substance in the brain, and how are they arranged! What is the white substance? Of what is the gray substance composed? What is supposed in regard to it? What happens n motion, and what in sensation