A text-book of the diseases of the ear / by Josef Gruber ; translated from the second German edition by special permission of the author, and edited by Edward Law and by Coleman Jewell.

Date:
1890
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of the diseases of the ear / by Josef Gruber ; translated from the second German edition by special permission of the author, and edited by Edward Law and by Coleman Jewell. 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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    each other, with but little diploe intervening, whilst at the lower and posterior part they suddenly and very strikingly separate from each othei. The inner lamella (Fig. 2, i) is considerably shortei than the external at the posterior two-thirds of the bone, and shows much more distinctly the horizontal direction than the external (Fig. 2, a). A furrow or sulcus, opening inwards, is thus left between them, and this will piesently be more closely considered. The whole squama is bounded by an irregular margin, which in the case of the perpendicular plate is almost semicircular in shape. Heie also it is sharp, on account of the deficiency of the internal lamella. In the horizontal part this margin presents a somewhat zigzag outline, so that two processes—an anterior and a posterior (Fig. 1, v and Ji)—are directed downwards, between which the central portion, concave inferiorly, has a well-marked horizontal direction. At the anterior process (at v) the two plates of bone are equal in length, and are joined by a somewhat rounded-off margin ; whilst at the posterior two-thirds, as has been already observed, the two lamellae are separated, and the outer lamella alone forms the lower margin of this process. On examining more closely the furrow (Fig. 2, above h), which opens inwards, and which is situated between the outer and inner lamellae of the horizontal squamous portion, it will be seen that the anterior part is bounded by smooth walls, whilst the posterior (Ji) exhibits the charac- teristics of osseous cellular spaces. As we shall subsequently see, the anterior part of this furrow helps to complete the tympanic cavity, while the posterior assists in the formation of the mastoid cells. The posterior extremity of the outer plate of the horizontal squamous portion, which assists in the formation of the mastoid cells, is described as the os epitym- panicum, and is said to exist as a separate little plate until the second month ol intra-uterine life. B. The tympanic ring (annulus tympanicus) consists of a bony ring, incomplete at its upper and posterior part, and which shows on its concave margin a well-marked furrow (sulcus tympanicus). The upper extremities of the ring are distant from each other from 1 to 2 mm.; but in exceptional cases they may be in contact, and thus complete the osseous circle. The anterior extremity of the tympanic ring makes, at an early period, a slight twist on its longitudinal axis; so that the internal lip, which bounds the sulcus tympanicus, is visible when the bony ring is seen in its natural connection with the squama. 1 he ring as a whole has a somewhat spiral direction. Hyrtl states that he possesses the temporal bone of an adult in which two tympanic rings exist (Handbuch der topographischcn Anatomic in ihrer praktischen und chirurgischen Anwendung, IV. Auflage, p. 248).