Cochlear development in human fetuses aged 12-22 weeks. Serial sections of human embryos and fetuses from the 12th to 22nd weeks of development were studied for the presence of the inner ear components. The first indication of the otic vesicle is evident at the stage of 14 mm CRL. By the 15th week the size and general shape of the vesicle are established. Up to the 17th week the lumen is relatively uniform in size. The cochlea length is about 3 mm at this stage and the oval window appears well defined. Later, an increase in both cochlea length and oval window diameter is observed as well as an improvement in the cochlea lumen shape. The spiral ganglion neurites appear in close association with the spiral ligament (SL) between the 14th and 18th week and the cochlear nerve is present on the 19th week of development. Cochlear ganglion cells begin to appear in the 15th week. From the 16th week on their number increases and by the 23rd week the whole organ is richly supplied with ganglion cells. At birth the human cochlea is not fully mature, however, it can be recognized that the inner ear development progresses in a pattern similar to that in other vertebrates.