Find Arvak's Skull

Background
While in the Soul Cairn, if the Dragonborn stays on the path leading to the Boneyard can find a soul frantically calling out, "Arvak, Arvak!" He will tell the Dragonborn how he and his loyal Arvak came to this realm and were attacked by monsters. He had told Arvak to run, and he says Arvak is still running and has been doing so for a long time. He begs the Dragonborn to find Arvak and disappears. Arvak's skull must be located in the Soul Cairn to free him.

Location
Arvak's skull can be found due east from the front gate of the Boneyard (where Valerica is found). It will be sitting on a pedestal surrounded by ghosts that turn into Mistmen. Once they are defeated the skull may be taken (or just grab the skull without defeating). After obtaining the skull, the soul who was looking for the horse will appear nearby, and he will teach the Dragonborn how to summon Arvak.