A monkey hangs st

Downward arrows are the weight and the upward arrows are friction

The weight of the monkey and the frictional force from the contact(which depends on the strength with which monkey is holding the vein, more the strength more the friction ), the friction will increase with normal force of vertical vein and the monkey hand and tail , act on the monkey. Weight acts on the full body but is felt by the contact parts , in this case it is monkey’s hands.

These are the two forces acting on the monkey.

It is in the vertical case only and also if the weight of the monkey is on the tail the there is a pulling force in the tail of the monkey also.