A complete dissection of a persistent stapedial artery and its companion venous sinuses revealed several noteworthy features. The proximal portion of the stapedial artery stem was missing, and the entire stapedial system was supplied through an anastomosis between the occipital artery and the ramus posterior of the stapedial artery; a similar type of collateral supply occurs in some xenarthrans and bats. The ramus posterior is a component of the primitive eutherian stapedial system and one that has not been reported previously in a primate. Both the anterior and posterior divisions of the ramus superior were present. The posterior division is identified here for the first time in a primate. The anterior and posterior divisions were accompanied by the cranio-orbital and petrosquamous sinuses, respectively. These sinuses were incomplete and attenuated relative to the primitive eutherian condition.