Melanosarcoma is composed of cells containing melanin pigments and frequently observed in gray horses. This is considered to be associated with the process of changes in the skin color with age from the dark color in ponies to white due to transfer of melanin pigments to the dock and shoulders. This specimen was obtained from a 15-year-old female gray horse with lesions in the dock and left kidney, below the costal pleura, and in the lumbar muscles and lumbar vertebral cavity. The black lesion indicate this tumor. (register No. 0025)

Masanobu Goryo
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Department of Veterinary Pathology, Faculty of Agriculture, Iwate University., Morioka, 020-8550, Japan