Henry Gray (18251861). Anatomy of the Human Body. 1918.
effected by a fold which extends deeply into the proximal part of the ductus endolymphaticus, with the result that the utricle and saccule ultimately communicate with each other by means of a Y-shaped canal. The saccule opens into the cochlear duct, through the canalis reuniens, and the semicircular ducts communicate with the utricle.
FIG. 901 Median views of membranous labyrinth and acoustic complex in human embryos. X 25 dia. (Streeter.) (See enlarged image)
FIG. 902 Transverse section through head of fetal sheep, in the region of the labyrinth. X 30. (After Boettcher.) (See enlarged image)
The mesodermal tissue surrounding the various parts of the epithelial labyrinth is converted into a cartilaginous ear-capsule, and this is finally ossified to form the bony labyrinth. Between the cartilaginous capsule and the epithelial structures is a stratum of mesodermal tissue which is differentiated into three layers, viz., an outer, forming the periosteal lining of the bony labyrinth; an inner, in direct contact with the epithelial structures; and an intermediate, consisting of gelatinous tissue: by the absorption of this latter tissue the perilymphatic spaces are developed. The modiolus and osseous spiral lamina of the cochlea are not preformed in cartilage but are ossified directly from connective tissue.
FIG. 903 Transverse section of the cochlear duct of a fetal cat. (After Boettcher and Ayres.) (See enlarged image)