. Cunningham's Text-book of anatomy. Anatomy. 848 THE OKGANS OF SENSE. which is especially developed towards the concavity of the tube. The membranous ampullae nearly fill the corresponding portions of the bony tubes, but the diameter of the semicircular ducts is only about one-fourth of that of the osseous canals. Each semicircular duct consists of three layers, viz.: (a) an outer vascular and partly pigmented fibrous stratum which fixes the duct to the bony wall; Perilymphatic space Macula acustica. Cuticular wall Fibres of the ramus recessus utriculi Fig. 722.—Vertical Section of the Wall o
. Cunningham's Text-book of anatomy. Anatomy. 848 THE OKGANS OF SENSE. which is especially developed towards the concavity of the tube. The membranous ampullae nearly fill the corresponding portions of the bony tubes, but the diameter of the semicircular ducts is only about one-fourth of that of the osseous canals. Each semicircular duct consists of three layers, viz.: (a) an outer vascular and partly pigmented fibrous stratum which fixes the duct to the bony wall; Perilymphatic space Macula acustica. Cuticular wall Fibres of the ramus recessus utriculi Fig. 722.—Vertical Section of the Wall of the Recessus Utriculi with the Macula Acustica and the bundles of nerve fibres. (b) an intermediate, transparent tunica propria, presenting a number of papiiliform elevations which project towards the lumen. The fibrous layer and tunica propria are thinnest along the attached surface of the duct, and in this region also the papiiliform elevations are absent; (c) an internal epithelial layer, composed of pavement cells. In the ampullae the tunica propria is much thickened, and projects into the cavity as a transverse elevation, termed the septum transversum, which, when seen from above, is somewhat fiddle-shaped; its most prominent part is covered by acoustic epithelium forming the crista ampullaris, at each end of which is a half-moon-shaped border of small columnar cells, the planum semilunatum. The cells covering the crista ampullaris consist of supporting cells and hair cells, and are similar in their arrangement to those in the maculae of tbe utricle and saccule; the hairs of the hair cells are, however, considerably longer, and project as far as the middle of the ampullary lumen. In fresh specimens they appear to end free, but in hardened preparations are seen to terminate in a soft, clear, dome-like structure, the cupula terminalis, which is striated, the striae converging towards its concavity. The nerves form arborisations around the bases of the bair cells. Membran
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
