Cochlear hair cells play a central role in the transduction of sound into neural output. Anatomical
descriptions of these cells, and their protruding hair bundles, are of fundamental interest since hair cell
transduction is dependent on hair bundle micromechanics and hair bundle micromechanics depends on hair
bundle morphology. In this paper, we describe quantitatively changes in the staircase profile of the hair
bundle along the apical portion of the chick's basilar papilla. Images of hair cells from 8 discretely dissected
segments of the apical 3rd of the basilar papilla were archived, and the profile contour outlined by the tips
of the stereocilia was digitised and curves were fitted by linear and power equations. The hair bundles of tall
hair cells exhibited both linear and curvilinear profiles, which were equally distributed along the papilla. All
short hair cells in our sample had straight contours. The differences in hair bundle shape among the tall hair
cells may lead to differential susceptibility to injury and some variance in the current-displacement
transduction curves due to differences in the translation of forces throughout the hair bundle.