The portion of the continental margin that serves as the boundary between oceanic crust and continental crust is the continental slope.

Here's a breakdown:

* Continental Shelf: The gently sloping, submerged portion of the continent that extends out from the shoreline.

* Continental Slope: A relatively steep drop-off that marks the transition from the continental shelf to the deep ocean floor. This is where the continental crust ends and the oceanic crust begins.

* Continental Rise: A gently sloping apron of sediment that accumulates at the base of the continental slope.

Let me know if you'd like more details about the continental margin!