. Cunningham's Text-book of anatomy. Anatomy. Section through promontory Lamina spiralis ossea secundaria Fissura vestibuli Lamina spiralis ossea Recessus cochlearis of vestibule Fig. 718. Modiolus Scala vestibuli Lamina spiralis ossea Scala tympani Tractus spiralis foraminosus Internal acoustic meatus -Section of Bony Cochlea. Area vestibularis superior Area n. facialis basal coil the upper surface of the lamina spiralis ossea forms almost a right angle with the modiolus, but the angle becomes more and more acute on ascending the tube. In the lower half of the basal coil a second smaller bony
. Cunningham's Text-book of anatomy. Anatomy. Section through promontory Lamina spiralis ossea secundaria Fissura vestibuli Lamina spiralis ossea Recessus cochlearis of vestibule Fig. 718. Modiolus Scala vestibuli Lamina spiralis ossea Scala tympani Tractus spiralis foraminosus Internal acoustic meatus -Section of Bony Cochlea. Area vestibularis superior Area n. facialis basal coil the upper surface of the lamina spiralis ossea forms almost a right angle with the modiolus, but the angle becomes more and more acute on ascending the tube. In the lower half of the basal coil a second smaller bony plate, the lamina spiralis secundaria, projects from the outer wall of the cochlea towards the lamina spiralis ossea, without, however, reaching it. If viewed from the vestibule the slit-like fissura vestibuli, already referred to (p. 844), is seen between the two laminae. A membrane, the membrana basilaris, stretches from the free edge of the lamina spiralis ossea to the outer wall of the cochlea, and completes the septum between the scala vestibuli and scala tympani, but the two scalae communicate with each other through the opening of the helicotrema at the apex of the cochlea. The scala tympani begins at the fenestra cochleae, which is closed by the secondary tympanic membrane (vide p. 833). At the commencement of the scala tympani a crest, termed the crista semilunaris, stretches from the attached margin of the lamina spiralis ossea towards the orifice of the fenestra cochleae. Close to this crest is seen the inner orifice of the aquaeductus cochleae, a canal measuring from 10 to 12 mm. in length, and opening on the under surface of the petrous part of the temporal bone medial to the fossa jugularis. Through it a communica- tion is established between the scala tympani and the subarachnoid cavity, and through it, also, a small vein passes to join the inferior petrosal sinus. The scala vestibuli, the higher of the two passages, begins in the vestibule ; its diameter in the
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
