. Biology of the Heteromyidae. Heteromyidae. 284 LAY. Fig. 11. —Morphological change in the Organ of Corti of D. merriami from the second half turn to the apex. Sections numbered 3, 5 and 7 are printed in reverse to facilitate comparisons. Numbers 2 through 7 are identical with the same numbers in Fig. 8. Black arrowheads = attach- ment of basilar membrane to osseous spiral lam- ina and spiral ligament. Note the progressive in- crease in width from 2 to 7. tions I have studied it is clear that the tectal cells largely rest atop Henson's cells, which have apical processes directed toward the sp
. Biology of the Heteromyidae. Heteromyidae. 284 LAY. Fig. 11. —Morphological change in the Organ of Corti of D. merriami from the second half turn to the apex. Sections numbered 3, 5 and 7 are printed in reverse to facilitate comparisons. Numbers 2 through 7 are identical with the same numbers in Fig. 8. Black arrowheads = attach- ment of basilar membrane to osseous spiral lam- ina and spiral ligament. Note the progressive in- crease in width from 2 to 7. tions I have studied it is clear that the tectal cells largely rest atop Henson's cells, which have apical processes directed toward the spiral ligament (Fig. 9). It is not possible to comment on the tunnel floor cells until thin sections are prepared. The elaboration of the tectal cells upon the Henson's cells effectively increases the height of the Organ of Corti above the bas- ilar membrane. Height increases three to four fold from the first turn to the second or third turns then declines toward the apex (Webster and Webster, 1977). Relative height is greatest and sustained over the greatest length on the basilar membrane in Microdipodops. Perognathus, Chaetodipus and Dipodomys are similar to one another and somewhat less developed than Micro- dipodops. Liomys and Heteromys lack a tec- tal canopy and the height of the Organ of Corti produced by Henson's cells, not tectal cells, changes little but reaches a maximum in the second turn thereafter declining to- ward the apex. The development of a tectal canopy results in a major increase in Organ of Corti height in the second and third turns relative to the conservative condition of Liomys and Heteromys. The cross sectional area of the scala tym- pani exhibits a striking localized constric- tion in Chaetodipus, Liomys, and Hetero- mys. The cross sectional areas of both perilymphatic chambers are approximately equal at any point along the basilar mem- brane in most species of mammals that have been studied and such is the case for Mi- crodipodops, Dipodomys and Pe
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