ANATOMY OF THE EAR  
The membranous labyrinth

The membranous labyrinth

Description : The membranous labyrinth, which is filled with endolymph, consists of the utricle, the saccule, the three semi-circular ducts and the cochlear duct.

The space between the membranous and bony labyrinths is filled with perilymph.

Each of the three membranous semi-circular ducts-the horizontal (lateral), the superior (vertical) and the posterior saemicircular canal contains a bulbous swelling (the ampulla). A tiny sense organ, the crista (Fig. 3.21) is situated within each ampulla.

The utricle receives the five openings of the semicircular ducts and communicates with the saccule. Both the saccule and the utricle also contain sense organs (the maculae).

The cristae and the maculae contain modified sensory neuroepithelium which is innervated by branches of the vestibular nerve. Ducts from the utricle and the saccule join to form the endolymphatic duct which terminates under the dura on the posterior surface of the petrous temporal bone as a dilatation-the endolymphatic sac.

Reissner's membrane runs obliquely from the osseous spiral lamina to the lateral wall of the bony labyrinth, dividing the cochlear duct from the scala vestibuli).
The ductus reuniens connects the lower part of the saccule to the cochlear duct, which then spirals upwards, ending blindly at the apex.

The cochlear duct (the scala media) divides the cochlea into the scala vestibuli and the scala tympani.

The basilar membrane extends from the osseous spiral lamina to the outer wall of the bony labyrinth.

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