ANTERIOR ASPECT OF HEAD AND NECK. 



sphaericus) for the saccule lies anteroinferiorly and contains 

 many foramina (macula cribrosa media) for the auditory 

 nerve. Above and behind this is an oblique ridge (crista ves- 

 tibuli) which ends anteriorly in a prominence (pyramid), but 

 divides behind to enclose a depression (recessus cochlearis). 

 A depression (recessus ellipticus) for the utricle lies above and 

 behind the crista, extending onto the roof and containing many 

 foramina (macula cribrosa superior). Below and behind this 

 is the orifice of a canal, the aqueductus vestibuli. Posteriorly 

 it presents the five orifices of the semicircular canals; and 

 anteriorly an elliptical opening into the scala vestibuli of the 

 cochlea. Its floor presents anteriorly a narrow cleft (fissura 

 vestibuli) ; this leads into the cochlea between a thin bony 

 lamella (lamina spiralis ossea) arising just external to the 

 recessus sphsericus, and another lamella (lamina spiralis secun- 

 daria) projecting from the outer wall of the cochlea. [759] 



The semicircular canals are three in number; each forms 

 two-thirds of a circle and has one end dilated (ampulla) . The 

 superior is vertical and transverse to the long axis of the 

 petrous bone. Its ampulla opens into the vestibule high up; 

 its other end joins that of the posterior canal, forming the crus 

 commune which opens into the upper and inner part of the 

 vestibule. The posterior is vertical and at right angles to the 

 superior. Its ampulla opens into the lower and back part of the 

 vestibule ; its upper end joins the crus commune. The external 

 is almost horizontal ; its ampulla opens into the vestibule just 

 above the fenestra ovalis. [760] 



The cochlea is conical, with its base over the bottom (area 

 cochleae) of the internal auditory meatus, and its apex (cupola) 

 directed forward and outward. It consists of a canal making 

 about two and a half coils around a conical central pillar (mo- 

 diolus) whose apex does not quite reach the cupola; in the 

 modiolus are canals for nerves. A thin bony shelf (lamina 

 spiralis ossea) winds around the modiolus and projects about 

 half-way into the cochlear tube; it incompletely divides the 



[101] 



