Cerberus was known as the hound of Hades. This three headed dog was the offspring of Echidna and Typhon. He had three heads, a serpent tail, and snakes coming out of some of his body parts.
The Cerberus was three headed but not all the time when written or talked about. He was related to many species that had many heads. Cerberus father had many snake heads who was called Typhon. Echidna, who was his mother, was half snake. The Cerberus was the brother of other multi-headed monsters that include Lernaean Hydra, Orthrus, and a two headed dog that guarded the cattle of Geryon.
The other one was Chimera who had the three heads of a lion, goat, and a snake. Cerberus was the only rare multi-headed animal talked about that had a few too many heads. In Hesiods Theogonay the Cerberus had fifty heads. Pindar gave the Cerberus one hundred heads. Many writers later on would give the Cerberus three heads.
There is one story by the poet Horace where the Cerberus has one dog head and a hundred snake heads. In Appollodorus the Cerberus has three heads with a bunch of snakes. In the story of the poet John Tzetzes the Cerberus had fifty heads of which three were of a dog and the rest of many beasts. In art from back then the Cerberus is often depicted with having only two heads or just one head. In 590 bc to 580 bc the Cerberus in the Corinthian cup of Argos had only one head.
When the Cerberus started showing to have three heads was in the mid sixth century BC on the Laconian cup. The Cerberus was usually depicted as having a snake or dog body with the heads and tails being of that sort. There were other cases were the Cerberus had three bodies that went with the three heads and had three tongues as well. In a Heracles story the Cerberus would vomit out bile which the poisonous aconite plant grew from. The vomiting started when the Cerberus was being taken out the underworld by Heracles.
On some accounts the Cerberus would have fire coming out his mouth or a foam of poison that would come out. They never would say what kind of breed of canine the Cerberus was, but if they can't refer to the Cerberus as a Hell Hound then it was a Hound.
The Cerberus was made up of canine, lion, goat, and snake in many stories.