首楞嚴義疏注經 1.379

1.379

若汝於身立中位者，身有中邊，若居身中，與內何別？應合見內。若就身邊，邊則非中，便有自語相違過也。

If you establish an intermediate position within the body, the body has a middle and boundaries. If it is in the middle of the body, how does that differ from being inside? It ought then to see inside. If it is in reference to the body's boundaries, the boundaries are not the middle, and there is then the fault of self-contradiction.