The spectral image cubes obtained by the Near-Infrared Mapping Spectrometer (NIMS) on Galileo as it flew by Venus have been analyzed to constrain the vertical structure of the clouds, the nature of the aerosol particles, and the location and particle properties of the opacity variations responsible for high-contrast features observed in the near-infrared windows at 1.7 and 2.3 μm. A radiative transfer program was used to simulate mid-latitude curves of limb darkening at 3.7 μm. Best-fit models to these curves demonstrate that the upper clouds are dominated by mode 2 particles (r = 1.0 μm), with a contribution of 15% of opacity from mode 1 particles (r = 0.3 μm). The low-latitude upper cloud is well represented by a dual scale-height model, with a particle scale height of 1 km from an altitude of 61-63 km, and a scale height of 6 km above this, up to the level where τ = 1 at approximately 71 km. This model also successfully simulates limb-darkening curves at 11.5 μm from the Pioneer Venus Orbiter Infrared Radiometer. Successful simulations of correlation plots of 1.7 vs 2.3 μm intensities reveal that mode 3 particles (r = 3.65 μm) represent the dominant source of opacity in the lower and middle clouds, and that variation in total cloud opacity reflects chiefly the addition and removal of mode 3 particles near the cloud base. We find that the full spectrum of brightnesses at 1.7 and 2.3 μm implies that the total cloud optical depth varies from 25 to 40.