This creates a powerful clamp-like grip between the first and third digits. They can move upright on top of as well as upside down under branches. A female Potto and Slow Loris in fact signals that she is ready to mate by hanging from her feet. Thus the exchange of oxygen and waste materials in the muscles continues even though there is no bodily movement. Special blood vessel storage channels in their hands and feet allows blood to flow freely.
All digits have nails, except the second toe of the foot which has a toilet claw used for grooming.
They also have extremely flexible bodies. Lorises have more vertebrae in their backs and the most vertebrae of primates, so they can twist every which way to slip silently through thick undergrowth. Their spine moves sinuously as they slowly change their grip. Their wrists and ankles are more flexible. Their hip and ankles joints are also more mobile than those of other primates.