Cerebellum

“ The cerebellum may be regarded as the physiological and the cerebrum as the psychic brain, for the cerebellum is void of intelligence and volition, but has important influences on the body. It may be considered, like the spinal cord, an intermediate structure between the controlling and conscious brain and the corporeal organs. ”

“ The cerebellum has its unconscious action in the processes of respiration and in the involuntary movements which are made in response to the senses, as in winking, starting back at a sound, etc. The cerebrum acts automatically in oases familiar to all. A large part of our mental activity consists of this unconscious brain work. There are many cases in which the mind has obviously reasoned more clearly and more successfully in this automatic condition, when left entirely to itself, than when we have been cudgeling our brains, so to speak, to get the solution. ”

“ With a passing mention of the cerebellum, the three-lobed organ shown in Diagram 61, and seen again in a more advanced stage in Diagram 63, we may dismiss the two hinder divisions of the brain.
The cerebellum lies on the upward path of fibres from the cord to the higher centres in the fore-brain. It is a somewhat complicated organ, and its functions are not yet fully known. The older physiologists took a very extreme view of its importance, assigning to it, among other romantic duties, that of providing a habitation for the soul. ”

“ In fishes the cerebellum and cerebral hemispheres are minute, and the intermediate or optic lobes very large: in the reptiles the cerebral hemispheres exceed the optic lobes, while the cerebellum is smaller. In birds the cerebellum becomes complex and the cerebrum greatly increases. In mammals the cerebellum increases in complexity or number of parts, the optic lobes diminish, 156while the cerebral hemispheres become wonderfully complex and enlarged, bringing us to the highest development, in man. ”

“ They reminded him of the fireflies of the green hells he had been in during the war.
"You are now skirting the convolutions of the cerebellum," his guardian angel told him. "They are electronic tubes which receive sensory impressions and translate them into impulses for cerebration. Here in the cerebellum the bulk of the associations is being evoked; these are then distributed throughout the hemispheres of the cortex or higher brain. Oh I do wish you wouldn't get seasick, Dr. Lee; some of our visitors do, you know; it's those wavy, wavy movements." ”

“ In the lower placental mammals, the cerebral hemispheres leave the proper upper and posterior face of the cerebellum completely visible, when the brain is viewed from above, but, in the higher forms, the hinder part of each hemisphere, separated only by the tentorium (p. 117) from the anterior face of the cerebellum, inclines backwards and downwards, and grows out, as the so-called "posterior lobe," so as at length to overlap and hide the cerebellum. ”

“ The white matter is more abundant in the hemispheres than in the median lobe, and is for the most part directly continuous with the fibres of the peduncles of the cerebellum. Thus the restiform or inferior peduncles pass from below upward through the white core, to end in the grey matter of the tentorial surface of the cerebellum, more especially in that of the central lobe ”

“ This [348] increase has affected principally the surface of the roof, so that as the cerebellum has grown it has been thrown into many folds, the exact form of which varies in different specimens. The cerebellum has at the same time increased in size and has thus extended laterad as well as caudad and craniad. It thus touches the cerebrum in front (separated from it by the tentorium) and aids it in concealing the midbrain and ’tween-brain in dorsal view, while caudad in the same view it conceals the greater part of the medulla. ”

“ With animals that run immediately upon birth, the cerebellum is much more powerfully developed than with animals that are born blind, are helpless, and that learn to walk with difficulty. Accordingly, and in consequence of its connection with the cerebrum, subcortical center and the spinal cord, the cerebellum is a station of the muscular and of the chief nervous system, by means of both of which qualities we keep our equilibrium. ”

“ What the facts indisputably prove is that the cerebrum has an important part in the mechanism by which the most complex psychical combinations are effected, and that the cerebellum has an important part in the mechanism by which the most complex muscular combinations184 are effected. The supreme importance of the cerebrum may be inferred from its dominating all the other centres, and from its preponderance in size. In man it stands to all the other cranial centres together in the relation of 11 to 3. ”

“ Independent masses of grey matter are, however, found in the interior of the cerebellum. If the hemisphere be cut through a little to the outer side of the median lobe, a zigzag arrangement of grey matter, similar in appearance and structure to the nucleus of the olivary body in the medulla oblongata, and known as the corpus dentatum of the cerebellum, is seen; it lies in the midst of the white core of the hemisphere, and encloses white fibres, which leave the interior of the corpus at its inner and lower side. ”

“ The disposition of the fibres in the brain is far too complex to be accurately followed. All that we can say is, that there are strands which connect one convolution with another, strands which connect one hemisphere with another, strands which connect cerebrum with cerebellum, and strands which connect the cerebrum with the lower ganglia. It is important to conceive this distinctly; for we shall hereafter see that the function of the Brain (by brain is here meant both Cerebrum and Cerebellum) is not that of innervation, but of incitation and regulation. ”

“ A line drawn along the edge of the cerebral hemisphere in Fig. 1, where that hemisphere overlies the cerebellum, will be seen to be much less nearly horizontal than a line is which holds the same relation in a human brain. It seems as if the cerebellum had encroached upon the cerebral lobes which roofed it over.
The same figure shows that a similar stunting has befallen the upward growth of both the frontal and posterior lobes, a line bounding the superior edge of the hemispheres from D forwards to A, describing a much more even curve than is usual in man. ”

“ From it in turn come a great many connecting nerve cells whose axons pass along the spinal cord and form nerve junctions with the motor nerve cells; and so nervous disturbances coming from the cerebellum can arouse the muscles to activity. We all know that walking or any other locomotor act, after it has once been learned, is carried on successfully without our performing any intellectual work in connection with it. What we do have to do is to start the act, and this is done through a discharge from the cerebrum ”

“ In man, the cerebrum presents an immense preponderance in weight over other portions of the brain; in some of the lower animals, the cerebrum is even less in weight than the cerebellum. Another interesting point is the development of cerebral convolutions in certain animals, by which the relative amount of gray matter is increased. In fishes, reptiles, and birds, the surface of the hemispheres is smooth ”

“ The cerebellum, as is well known, is not considered by our contemporary physiology to have any special connection with consciousness, but is treated as a co-ordinator of sensory and locomotor functions exclusively. Most physiologists, however, readily admit that the functions of this large and complicated organ are still very obscure. Dr. Courmont's book is assuredly the most systematic attempt yet made to throw light into the darkness. He believes that the evidence points to a distinct psychic function for the cerebellum. ”

“ Spurzheim gives a view of the brain of the pike with an optic lobe partially opened, to show the ventricle.
The cerebellum or physiological brain is formed on the same general plan, having its energetic or forcible functions in the posterior inferior regions, and its more sensitive functions located anteriorly.
In the embryo of twelve weeks a great advance has taken place; the optic lobes or quadrigemina are still large, but the cerebrum is larger than all the remainder. ”

“ At first the cerebellum is smooth, but as it develops, its fissures become greater and greater, thus increasing its cortex, which presides over the muscular movements. With the developing cerebellum are associated increasing powers of muscular co-ordination; increasing delicacy and complexity of muscular movements. ”

“ Caudad to the cerebrum are seen the end of the paraphysis, G.p., the optic lobes, MH, and the cerebellum, HH. From the cerebral peduncles (ventrad to the optic lobes) arises the oculomotor nerve, III, and dorsocaudad to this, between the optic lobe and the cerebellum, arises the trochlear nerve, IV. From the middle zone (in a dorsoventral direction) of the medulla, ventrad to the cerebellum, arises the very large trigeminal nerve, V; while from its usual place, on the ventral surface of the medulla, the abducens nerve, VI, takes its origin by several roots. ”

“ From such simple beginnings as are seen in Ammocœtes, the higher forms of brain have been evolved, to culminate in that of man, in which the massive cerebrum and cerebellum conceals all sign of the dorsal membranous roof, those parts of the simple epithelial tube which still remain being tucked away into the cavities to form the various choroid plexuses. ”

“ From its small size, and from the imperfect development of the convolutions, this brain was, most likely, taken from a very young animal; the cerebral membranes have been removed; the vertex is somewhat flattened; the orbital surfaces have lost their characteristic concavity; the middle lobes have sunk asunder; and the cerebellum has, undoubtedly, been a little displaced backwards. ”

“ This is an important intermediate structure between the cerebrum and the cerebellum, and in fishes is the largest part of the brain, but in man is the smallest portion, as will be explained hereafter, and is the origin of the optic nerve, as well as a commanding head for the spinal system, from which convulsions may be produced. ”