Comparison of truncal and caudal lesions in the vertebral column of the sand rat (Psammomys obesus).

Caudal vertebrae of sand rats (Psammomys obesus) of two age-groups were examined histologically, and the findings were compared with those obtained previously in the truncal spines of these animals. Degenerative processes were basically similar in both locations, although they were somewhat attenuated in the tail. By contrast, the incidences of disk herniation and of spondylosis were much more common in the trunk than in the tail. We concluded that in the sand rat there is a common, probably systemic, denominator for disk degeneration at all sites, and suggest that this factor is related to the peculiar water and/or electrolyte metabolism of these desert animals. Factors causing herniation of the degenerated disk and spondylosis seem to be related to local stresses which, in the presence of marked disk degeneration, may not exceed physiological limits.