Scala Vestibuli Scala Tympani

Cochlear duct

Scala Tympani

Figure 16.3 A and B. Development of the otocyst showing a dorsal utricular portion with the endolymphatic duct and a ventral saccular portion. C to E. Cochlear duct at 6, 7, and 8 weeks, respectively. Note formation of the ductus reuniens and the utriculosaccular duct. F and G. Scanning electron micrographs of mouse embryos showing similar stages of development of the otocyst as depicted in A and B. Arrowheads, en-dolymphatic duct; S, saccule; small arrow, opening of semicircular canal; U, utricle. G also shows initial stages of cochlear duct formation (large arrow).

Figure 16.3 A and B. Development of the otocyst showing a dorsal utricular portion with the endolymphatic duct and a ventral saccular portion. C to E. Cochlear duct at 6, 7, and 8 weeks, respectively. Note formation of the ductus reuniens and the utriculosaccular duct. F and G. Scanning electron micrographs of mouse embryos showing similar stages of development of the otocyst as depicted in A and B. Arrowheads, en-dolymphatic duct; S, saccule; small arrow, opening of semicircular canal; U, utricle. G also shows initial stages of cochlear duct formation (large arrow).

acusticae, develop in the walls of the utricle and saccule. Impulses generated in sensory cells of the cristae and maculae as a result of a change in position of the body are carried to the brain by vestibular fibers of cranial nerve VIII.

During formation of the otic vesicle, a small group of cells breaks away from its wall and forms the statoacoustic ganglion (Fig. 16.2C). Other cells of this ganglion are derived from the neural crest. The ganglion subsequently

Ganglion Shell

Figure 16.4 Development of the scala tympani and scala vestibuli. A. The cochlear duct is surrounded by a cartilaginous shell. B. During the 10th week large vacuoles appear in the cartilaginous shell. C. The cochlear duct (scala media) is separated from the scala tympani and the scala vestibuli by the basilar and vestibular membranes, respectively. Note the auditory nerve fibers and the spiral (cochlear) ganglion.

Figure 16.4 Development of the scala tympani and scala vestibuli. A. The cochlear duct is surrounded by a cartilaginous shell. B. During the 10th week large vacuoles appear in the cartilaginous shell. C. The cochlear duct (scala media) is separated from the scala tympani and the scala vestibuli by the basilar and vestibular membranes, respectively. Note the auditory nerve fibers and the spiral (cochlear) ganglion.

splits into cochlear and vestibular portions, which supply sensory cells of the organ of Corti and those of the saccule, utricle, and semicircular canals, respectively.

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