Cynocephalus (Gr.) The Egyptian Hapi. There was a notable difference between the ape-headed gods and the “Cynocephalus” (Simia hamadryas), a dog-headed baboon from upper Egypt. The latter, whose sacred city was Hermopolis, was sacred to the lunar deities and Thoth Hermes, hence an emblem of secret wisdom—as was Hanuman, the monkey-god of India, and later, the elephant-headed Ganesha. The mission of the Cynocephalus was to show the way for the Dead to the Seat of Judgment and Osiris, whereas the ape-gods were all phallic. They are almost invariably found in a crouching posture, holding on one hand the outa (the eye of Horus), and in the other the sexual cross. Isis is seen sometimes riding on an ape, to designate the fall of divine nature into generation.
Source: H.P.Blavatsky - The Theosophical Glossary