Posselts envelope of motion:
Described by Dr. Posselt
He described 3dimensional movement of mandble in 3planes
1. Sagittal
2. Frontal
3. Horizontal
these movements are called border movements as they detail the maximum movement of mandible in all these 3 planes

The shape of posselt's envelop of motion in each plane is:
Sagittal Beak shaped
Frontal Shield shaped
Horizontal Diamond shaped