13
PALEOBIOS, VOL 21, NUMBER 2, SEPTEMBER 2001
Fig. 1. Dorsal (left) and ventral (or palmar; right) views of I.ACM 144725. Scale bar     1
either arthritis (an infectious process) or arthrosis (a non-
infectious process).
The pathogenesis of non-articular periostoses of this type
in equids has been discussed by Rooncy (1997). In general
these lesions are related to avulsion of ligaments from their
bony attachments as a result of instability and jerky, irregu-
lar movements of the affected leg or leg segment (Rooncy
and Robertson 1996). Such instability usually results from
misplacement of the foot on a surface.
ACKNOWLEDGEMENTS
The authors thank Samuel A. Mcl-cod and Gary T.
Takcuchi of the Natural History Museum of Los Angeles
County, who provided LACM 144725. Thanks are also ex-
tended to volunteers Alex and Matthew Van Dam of the
Natural History Museum of Los Angeles County, who or-
ganized the collection of fossil horses from San Josccito
Cave and discovered the specimen.
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14
Fig. 2. Radiograph of LACM 144725 in dorsal view. The negative image (original radiograph) is on the left; positive on the right.
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