Not everyone agrees that Cerberus has three heads. For 10 points each:
[10m] On Attic vases, Cerberus is usually depicted with only two heads, making him more like this other dog who guarded Geryon's cattle.
ANSWER: Orthus [or Orthrus]
[10h] The earliest description of Cerberus by this author describes him with fifty heads. The Megala Erga and Megalai Ehoiai are poems in this author's corpus similar to more famous works by him.
ANSWER: Hesiod (The Megala Erga and Megalai Ehoiai are similar to Works and Days and Catalogue of Women respectively)
[10e] The poet Horace described Cerberus as having one dog head and 100 heads of these animals. The hair of the Gorgons are these animals.
ANSWER: snake
<Lalit Maharjan , Mythology - Greco/Roman>