A total of 115 feet, which were proved to have no pathological changes either from gross or from histopathological examination, were collected from horses between 1 and 25 years of age. They were examined radiographic ally with the following results.
1. The foot increased in size with the advance in age until about 6 years. There were no remarkable changes after that.
2. The degree of enlargement or shrinkage revealed in radiographs taken from the lateral, dorsovolar, and volardorsal projections was presumed to be useful for determination of the positional relationship within the foot. The overlapping shadows of the third phalanx, and second phalanx, and lateral cartilage were seen in the dorsovolar projection.
3. In the dorsovolar projection, blur, roughness. and serration were noted on the distal border of the third phalanx, and various shadows were seen inside. In the lateral projection, blurred compact parts and various shadows of bone trabeculae were seen.
4. The degree of modification of the third phalanx was more pronounced in the hind limbs than in the forelimbs, as was clear from these radiographical findings. The external posterior angles were more pronounced than the internal.
5. There was a distinct difference in the radiographic findings of the third phalanx between horses less than 2 years of age and those above this age. In those horses, simple, moderately salient, and salient radiographs were distinguished.
6. Concerning the coarsenss, a considerably intimate relationship was found between the radiographical findings and the findings of such specimens of the third phalanx as cut along the median surface.
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