RESUMEN
The aim of the work was to make a systemic study of the variability of the human musculus peroneus tertius during the foetal period. Examination was made of 193 foetuses of ages ranging from 84 to 256 days after conception. The results obtained indicated that the musculus peroneus tertius was present in 83.16% of the human foetuses studied and that its intrauterine development was progressive and almost proportional. Previous studies have not revealed dimorphic or bilateral differences with respect to any of the features examined. On the basis of the examinations and bibliographical data a uniform typology of the musculus peroneus tertius variants was created and three final types were distinguished: the pithecogenic (44% cases), eugenic (34% cases) and progenic (22% cases).
