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The cerebrum, in addition to controlling the voluntary movements, is able to establish the necessary conditions for secondary reflex actions, such as walking, writing, etc. Although certain of the divisions of the nervous system exercise special functions, all parts of it are closely related. Exercises.—1. Give the function of each of the parts of a neuron.
The process of general enlargement and of progressive convolution are continued, and stages are reached and passed which correspond with the monkey and ape conditions. Nothing in human development is more impressive than the origin of the cerebrum and its development by passing through successive stages which are counterparts in the main of the adult brains of other and lower animals.
The centre in the cerebrum which controls the use of the hands is on the fringe of the region which seems to be concerned in mental operations. For reasons which will appear presently, we may add that the centres for controlling the muscles of the face and head are in the same region.
Hall gave an admirably clear and interesting account of his experiments and conclusions in a paper before the Royal Society, "On the Reflex Functions of the Medulla Oblongata and the Medulla Spinalis," from which, as published in the Transactions of the society for 1833, we may quote at some length: "In the entire animal, sensation and voluntary motion, functions of the cerebrum, combine with the functions of the medulla oblongata and medulla spinalis, and may therefore render it difficult or impossible to determine those which are peculiar to each; if, in an animal deprived of the brain, the spinal marrow or the nerves supplying the muscles be stimulated, those muscles, whether voluntary or respiratory, are equally thrown into contraction, and, it may be added, equally in the complete and in the mutilated animal; and, in the case of the nerves, equally in limbs connected with and detached from the spinal marrow.
As we survey the vertebrate sub-kingdom of animals, we find that as this surplus increases, the surface of the highest centres increases in area. In the lowest vertebrate animal, the amphioxus, the cerebrum and cerebellum do not exist at all. In fishes we begin to find them, but they are much smaller than the optic lobes.
For there is a very marked groove in every such skull, as in the human skull which indicates the line of attachment of what is termed the 'tentorium' a sort of parchment-like shelf, or partition, which, in the recent state, is interposed between the cerebrum and cerebellum, and prevents the former from pressing upon the latter.
During the sleeping hours, or during the waking hours of a busy professional life, the brain had, without my consciousness, been solving the difficulties. This experience is by no means a peculiar one. Many scientific workers have borne testimony to a similar habit of the cerebrum.
The former has its "root" above in the cerebrum, the latter has its roots in the heart. Along the trunks and branches run currents of "nervous ether" and "life" respectively, and the Science of Yoga teaches its disciples to use both of these forces for mystical purposes.
'A'. Cerebrum; 'B'. Cerebellum. The former drawing is taken from a cast in the Museum of the Royal College of Surgeons, the latter from the photograph of the cast of a Chimpanzee's skull, which illustrates the paper by Mr. Marshall 'On the Brain of the Chimpanzee' in the 'Natural History Review' for July, 1861.
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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