The diseases of the ear and their treatment . fovea hemispherica {saccult) infront, and the recessus ellipticus or fovea hemi-elliptica iutriculi)behind. The external wall of the vestibule separates it from the 2o8 DISEASES OF THE INTERNAL EAR. tympanic cavity, and in this wall is situated the fenestra ovalis( Fig. 41), in which the foot-plate of the stapes is fastened bymeans of the annular ligament. In the internal wall of the vesti-bule are small orifices {macules), through which the branches of thevestibular nerve enter. The three semicircular canals, which areall situated at right ang
The diseases of the ear and their treatment . fovea hemispherica {saccult) infront, and the recessus ellipticus or fovea hemi-elliptica iutriculi)behind. The external wall of the vestibule separates it from the 2o8 DISEASES OF THE INTERNAL EAR. tympanic cavity, and in this wall is situated the fenestra ovalis( Fig. 41), in which the foot-plate of the stapes is fastened bymeans of the annular ligament. In the internal wall of the vesti-bule are small orifices {macules), through which the branches of thevestibular nerve enter. The three semicircular canals, which areall situated at right angles to each other, communicate with theposterior part of the vestibule by five apertures. We distinguishthe semicircular canals as follows—a horizontal (external) , andtwo vertical, the frontal (superior) , and the sagittal (posterior) These different canals commence with a dilated lumen, theampulla ; their extremities are of the actual width of the canal, andthe two vertical canals have a common termination. Anteriorly the Wer. Fig. 42. vestibule merges into the cochlea, the apex of which is directed out-ward. The cochlea makes two turns and a half around a centralpillar (modiolus), which lies horizontally. From the modiolus theso-called spiral lamina, also consisting of bone ( in Fig. 42,representing a vertical section through one of the windings of thecochlea), projects into the lumen of the cochlea, and is continuedto the opposite wall by means of the lamina spiralis membranacea,also called the viembrana basilaris (). The windings of thecochlea are thus divided into two parallel canals. The superior ANA TOMICAL. 209 canal commencing at the vestibule is named the scala vestibuli(); the inferior, communicating with the tympanum through thefenestra rotunda, is named the scala tympani (). The two canalscommunicate with each other through a small opening, the heli-cotrema. Corresponding with the division of the osseous vestibule, themembranous por
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