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This cortical or glandular substance constitutes the surface of the cerebrum, and also the surface of the corpora striata, from which proceeds the medulla oblongata; it also constitutes the middle of the cerebellum, and the middle of the spinal marrow.
The medulla oblongata, situated at the base of the brain where it joins the spinal cord, contains those brain centers that control the purely vegetative, vital functions: the circulation of the blood, the respiration, regulation of animal heat, etc.
Breathing is a reflex or involuntary act. The respiratory centre, consisting of an expiratory and inspiratory division, is situated in the bulb, or medulla oblongata, the portion of the brain just above the spinal cord.
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.
Although this quadrigeminum is very insignificant in man and the higher mammals, it forms a special third section, greatly developed in the lower vertebrates, the "middle brain." The narrow central canal of the spinal cord continues above into the quadrangular fourth cerebral cavity of the medulla oblongata, the floor of which is the quadrangular depression.
One of the most interesting problems is to find the ganglionic origin of the great nerves of the medulla oblongata, and this is the end to which, by the aid of the most delicate sections, colored so as to bring out their details, mounted so as to be imperishable, magnified by the best instruments, and now self-recorded in the light of the truth-telling sunbeam, our fellow-student is making a steady progress in a labor which I think bids fair to rank with the most valuable contributions to histology that we have had from this side of the Atlantic.
Hind-brain, cerebellum, medulla oblongata. d. Eye. e. Ear. f. First visceral arch. g. Second visceral arch. H. Vertebral columns and muscles in process of development. i. Anterior extremities. K. Posterior extremities. Man is developed from an ovule, about the 125th of an inch in diameter, which differs in no respect from the ovules of other animals.
Thus we find in the lowest order of fishes that all they possess of brain matter is a small protuberance at the end of the spinal cord. As the species and families rose in the scale of evolution, the brain developed proportionately from behind forward and became differentiated into three distinct divisions: the medulla oblongata, the cerebellum, and the cerebrum.
The head had to be balanced in such a way that through the pivot or joint on which it rests a safe passageway could be secured for one of the most delicate and most important of all the parts or structures of the human machine. We have never found a good English name for this structure, so we use its clumsy Latin one Medulla oblongata or medulla for short.
Lameness originating from nerve affection, may involve central structures as, for example, the spinal cord, medulla oblongata or parts of the brain. In making an examination of some lame animals it is necessary to distinguish between cases of lameness that are of central origin and marked by incoördination of movement, and disturbances caused by other affections.
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