File:Keith1902 fig042.jpg

From Embryology

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Fig. 42 A transverse section showing how the Walls of the Antrum are formed

The antrum of the mastoid represents the extreme outer or posterior end of the first cleft recess (Fig. 39 and Fig. 40). It is formed at the same time and in the same manner as the tympanum. Its use is unknown, but it has frequently to be exposed by the surgeon to remove the effects of chronic middle ear disease. At birth its outer wall is formed by the thin post-auditory part of the squamosal (Fig. 41 and Fig. 42). The squamosal forming its outer wall is then only 2 mm. thick, but every year until the 20 th, or later, this plate increases nearly 1 mm. in thickness, so that by the 20th year the antrum is buried by a plate of bone about 20 mm. thick.

There is a great individual variation, however, in the thickness of its outer wall. The antrum lies above and behind the level of the external auditory meatus ; the post-auditory spine and suprameatal triangle formed by the post-auditory part of the squamosal lie over it and serve as surface guides to it. The antrum opens in front into the attic of the tympanum. The tegmen tympani (Fig. 42) forms its roof and the petro-mastoid its floor and inner wall. The aqueductus Fallopii runs down the inner wall of its mouth (Fig. 43), and in its inner wall is situate the external semicircular canal. The petro-squamous suture in its roof (Fig. 42), and the masto-squamous suture on its outer wall (Fig. 14 B), become closed in the second year, and thus the escape of pus from it is rendered more difficult.

Development of the Organ of Hearing: Fig. 35. Cephalic region of an embryo, showing the origin of the Auditory System | Fig. 36 A. Adult External Auditory Meatus | Fig. 36 B. External Auditory Meatus at Birth | Fig. 37. Tubercles round the First Visceral Cleft to form the External Ear | Fig. 38. Part of the Adult Ear formed by each Tubercle | Fig. 39. Auditory Organs 6th week human fetus | Fig. 40. Cavities from the Inner Recess of the First Cleft | Fig. 41. The temporal bone at birth | Fig. 42. Walls of the Antrum | Fig. 43. Outer aspect of the Petro-mastoid at birth | Fig. 44. Membranous Labyrinth | Fig. 45. The Otocyst in an Embryo of five weeks | Fig. 46. Nerve Structures Sense of Hearing | Figures

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Human Embryology and Morphology (1902): Development or the Face | The Nasal Cavities and Olfactory Structures | Development of the Pharynx and Neck | Development of the Organ of Hearing | Development and Morphology of the Teeth | The Skin and its Appendages | The Development of the Ovum of the Foetus from the Ovum of the Mother | The Manner in which a Connection is Established between the Foetus and Uterus | The Uro-genital System | Formation of the Pubo-femoral Region, Pelvic Floor and Fascia | The Spinal Column and Back | The Segmentation of the Body | The Cranium | Development of the Structures concerned in the Sense of Sight | The Brain and Spinal Cord | Development of the Circulatory System | The Respiratory System | The Organs of Digestion | The Body Wall, Ribs, and Sternum | The Limbs | Figures | Embryology History


Keith A. Human Embryology and Morphology. (1902) London: Edward Arnold.

Cite this page: Hill, M.A. (2024, May 30) Embryology Keith1902 fig042.jpg. Retrieved from

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current02:40, 30 December 2013Thumbnail for version as of 02:40, 30 December 2013404 × 400 (21 KB)Z8600021 (talk | contribs)==Fig. 42 A transverse section showing how the Walls of the Antrum are formed== {{Keith1902_4_figures}} {{Human embryology morphology 1902 footer}}