Pottos cannot run. Like other lorisid primates they move by deliberate hand-over-hand climbing, with a grip strengthened by a specialised blood-vessel network in the limbs that allows sustained clinging with little fatigue. Speed is not available to them, so their defences are anchorage and armour.
The armour is the scapular shield: the spinous processes of the lower cervical and upper thoracic vertebrae are elongated and nearly break the skin, which is thickened and richly supplied with sensory nerves over them. A threatened potto lowers its head, exposing the ridge, and can drive it upward at a predator while keeping its feet locked to the branch.
The sensory role may matter as much as the physical one. The dense innervation of the shield suggests it works as a touch organ that detects a predator approaching from above, though this has not been tested directly, and the shield also features in social contact between pottos.