This British Medical Journal article and these responses to the first article describe instances of polydactyly in the paintings of Raphael. Raphael was noted for his meticulous attention to detail and the "perfection" of his paintings, so the presence of sixth toes cannot be viewed as a simple oversight or error on his part. Nor is the subject in the embedded photo an insignificant figure such as a random cherub - it's the infant John the Baptist. Polydactyly (extra fingers and/or toes) is an uncommon anomaly, but it is autosomal dominant (strongly inherited) and therefore the reason it appears in several different works by Raphael may be that the disorder affected a family used by Raphael as models for his paintings.