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In so far as certain other parts of the brain are concerned medulla, pons, mid-brain, basal ganglia cerebellum we who are human are not essentially superior to the dog, the cow, the elephant or the monkey.
First, it is the channel through which pass through lines of communication to and from the upper brain and the mid-brain on the one hand and the rest of the body on the other.
The brain of all except the very lowest vertebrates consists of four portions: 1. The cerebrum, or cerebral lobes, or simply "forebrain," the seat of consciousness, thought, and will, and from which no nerves proceed. Whether the primitive vertebrate had any cerebrum is still uncertain. 2. The mid-brain, which sends nerves to the eyes, and in this respect reminds us of the brain of insects.
But suppose that some playful comrade pours still more liquor down the victim's throat. The medulla, or lower brain, then becomes paralyzed, the vital organs cease to act and the man is no longer "dead" drunk. He has become a sacrifice to Bacchus. He is literally and actually dead. It seems, then, that the surface brain and mid-brain constitute together the organ of consciousness and will.
In mammals it extends upward and backward, has already in lower forms overspread the mid-brain, and is beginning to cover the small brain. But this was not so in the earliest mammals. Here the cerebrum was small, more like that of reptiles. But during the tertiary period the large brain began to increase with marvellous rapidity.
The cerebellum increases with the greater locomotive powers of the animal. But its development is evidently limited. The large brain, or cerebrum, is in fish hardly as heavy as the mid-brain; in amphibia the reverse is true. In higher recent reptiles the cerebrum would somewhat outweigh all the other portions of the brain put together.
This leaves the mid-brain without the check-rein of a reflective intellect, and the man will be senselessly hilarious or quarrelsome, jolly or dejected, pugnacious or tearful, and would be ordinarily described as "drunk." If in spite of this he keeps on drinking, the mid-brain soon becomes deadened and ceases to respond, and the cerebellum, the organ of equilibrium, also becomes paralyzed.
The next higher division, or mid-brain, is a large region from which the conscious will issues its edicts regulating all voluntary bodily movements. It is also the seat of certain special senses, such as sight. Lastly, the surface brain, known as the cortex, is the interpretative and reflective center, the abode of memory, intellect and will.
So that the correspondence in general structure, in the minute structure of the tissues, in chemical composition and in constitution, between man and the higher animals, especially the anthropomorphous apes, is extremely close. Shows a human embryo, from Ecker, and a dog embryo, from Bischoff. Labelled in each are: a. Fore-brain, cerebral hemispheres, etc. b. Mid-brain, corpora quadrigemina. c.
Its main seat is the cerebrum, the "highest" nervous tissue, whereas reflex and instinctive actions usually are in the vegetative nervous system, the spinal cord, the bulbar regions and the mid-brain, all of which are lower centers. Choice, which is intimately associated with inhibition, is par excellence a cerebral function and in general is associated with intense consciousness.
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