Postnatal changes in the size of the avian cochlear duct.

The length of the cochlear duct was measured in chicks aged embryonic day 14 to post-hatch day 469. Chicks were anesthetized, decapitated and their cochlear ducts exposed under an operating microscope. Because of the very thin bone and cartilage surrounding the relatively straight tube of the papilla the entire cochlear duct could rapidly be exposed and measured without fixation or removal from the head. The length of the duct was measured using a computer based Zeiss Videoplan Image Analysis System. A total 41% increase in length was seen from embryonic day 14 to post-hatch day 469; 20% of this increase occurred after hatching. It is suggested that this increase in cochlear duct length could influence basilar membrane properties important to frequency coding mechanisms during development.