The first pair of these cranial nerves are called the olfactory nerves; they go to that part of the nose in which the organ of smell is situated; they are the nerves by which the stimuli which cause the sensation of smell are conveyed to the brain.

These nerves do nothing else; no muscles are caused to contract by means of them and no other kind of sensation than that of smell is conveyed by them, so you see here we have a different class of nerves, all the spinal nerves having two properties; muscles were moved by means of them, and sensations were conveyed by means of them. The second pair of nerves start one from each side of the brain; they join one another, or rather are connected together by a band of nerve fibres, and then pass forwards, one to each eyeball. These are the nerves which belong to the sense of sight; they are called the optic nerves, because they convey the sense of sight to the brain, they do nothing else whatever. These first two pairs of nerves are examples of purely sensory nerves. The third pair are the nerves, by means of which most of the muscles which move the eyes are made to contract. The fourth and sixth pairs supply those muscles which move the eyeball, and which are not supplied by the third pair. In the third, fourth, and sixth pairs of nerves we have examples of nerves which only influence muscles.

The fifth pair of nerves are the largest pair of nerves which start from the brain, and they resemble spinal nerves in that each of them has two roots, - a motor root and a sensory root, with a ganglion upon the latter; they are mixed nerves, motor and sensory. They supply the skin of all the face, the mucous membrane of the mouth and nose, the teeth, and certain muscles of the upper and lower jaws.

I have mentioned the sixth pair already; the seventh pair of nerves are called the facial nerves, because they supply the muscles of the face; they are purely motor nerves.

The eighth pair were counted as part of the seventh pair by the old anatomists, and are the nerves which go to the organs of hearing, conveying the sensation of hearing from the organs of hearing to the brain; they are called the auditory nerves, and are purely sensory.

Now, I need not go on mentioning all these nerves, but the nerves of one more pair are so important that I must speak to you about them. One pair of the nerves which rise from the medulla oblongata, leave the brain and go to other parts of the body than the head; these nerves go by the name of the pneumogastric or the vagus nerves, from their wandering course; they supply the larynx in which the voice is formed, part of the pharynx, the windpipe, the oesophagus or gullet, the lungs, and going along by the oesophagus, pass through the diaphragm and supply the stomach; they also give branches to the heart. So you see that they are extremely important nerves. They go a long way, and supply important organs - the heart, the lungs, the oesophagus, the larynx, the stomach, and others, and that is one of the reasons why the medulla oblongata, from which they start, is such an extremely important part of the nervous system.

You may cut off the brain of an animal entirely, so long as you leave the medulla oblongata untouched, and he will go on living; he has no senses, but lives for some time, because this pair of nerves which supply the heart, the lungs, the stomach, etc., is left untouched.

Not only so, but fibres from all the cranial nerves, except the first two pairs, have been traced into the medulla oblongata.

The small brain has the property of co-ordinating the muscles on the two sides of the body; of causing the muscles of the body to act in concert with one another. When the small brain is injured the animal does not walk straight, but twists round and round.

The ganglia at the base of the brain are nerve centres, which are capable of acting independently of the will; they are connected with most of the nerves that belong to the brain.

Now, we know that reflex actions are capable of being performed by the spinal cord independently of the will; such actions are also capable of being performed by means of the nerves which belong to the brain. For instance, when we see a flash of lightning, or when a. lighted candle is passed near to our eyes, we wink unconsciously. And not only so, but if you pass something quickly in front of a person's eyes it will make him wink; he cannot help it, even if he tries to; so that is an action which occurs not only independently of, but even in spite of, the will, and is a purely reflex action. It is produced by the stimulus travelling along the optic nerves from the eyes to the ganglia at the base of the brain, causing the sense of something coming too near the eyes, upon which these ganglia at the base of the brain immediately start a stimulus along the nerves which go to the muscles of the upper eyelids, causing these muscles to contract and pull down the eyelids; that is a reflex action performed by the brain, and entirely independently of the will of the animal, so that these ganglia at the base of the brain are capable of originating actions, movements, without our knowing anything about it.