Clinical lectures on important symptoms. On giddiness / by Thomas Grainger Stewart.

  • Stewart Thomas Grainger, Sir, 1837-1900.
Date:
1884
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Licence: Public Domain Mark

Credit: Clinical lectures on important symptoms. On giddiness / by Thomas Grainger Stewart. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    but I think are real. I shall not dwell upon them, but the special sense for equilibriation, which has its seat in the semi-circular canals, requires fuller notice. Let me remind you of some anatomical facts and physio- logical explanations. The canals are situated in the petrous portion of the temporal bone. They are three in number, and communicate by means of five openings with the vestibule. Each canal has a dilated or ampullary end, and each by its ampuUary end opens into the vestibule, while two of them have their non-ampullary ends united, and communicate with the vestibule by a common opening. These canals occupy different planes, and are known as superior, posterior, and horizontal, according to their position. Within the bony labyrinth there is a membranous labyrinth, the membranes being much smaller than the canal, except at the ampullary ends. Between the bony canal and the membranes is the perilymph, with connective tissue, blood-vessels, and nerves. Within the membranous canal is the endolymph. A branch of the portio mollis of the seventh nerve is distributed to a crescent-shaped ridge near the middle of each ampulla. The terminal nerve-structures are hair-like cells, which project into the endolymph, and which must obviously be affected by changes in it. Through the chain of bones the labyrinth is connected with the tympanum. The handle of the malleus is fixed into the tympanum, while its head articulates with the incus. The latter, again, is connected with the stapes as well as with the posterior wall of the tympanum. The stapes is fixed into the fenestra ovalis, and by its movements produces alterations in the state of the fluids in the whole labyrinth. In 1828, Flourens discovered that the semi-circular canals have something to do with the maintenance of the equili- brium of the body. He found by experiment that section of a membranous canal was always followed by movements of the head, or even of the body, rotating about an axis at right- angles to the plane of the divided canal. On section of the horizontal canals, the animal moved its head rapidly from side to side, and tended to spin round on a vertical axis. When the posterior canals were cut, rapid movements back-