The mortise should not come too near the end, or the portion of wood outside it will shear out.
Hence the tenon is narrowed on the outside enough to insure strength in the mortised piece.

The rule is that the tenon should be one-half the width of the rail, minus the groove.

But enough of the tenon is left full width to fill up the groove at the outer end of the mortised piece.

This is called the _haunch_.

The width of the mortise is equal to the width of the groove, its length to the width of the tenon.
Before assembling the panel frame, put soap or tallow on the corners of the panel to prevent its being glued to the frame.
_No.43.Table or taper haunching_, Fig.267.Sometimes, as in table construction, for the sake of stiffening the rail, or in places where it is desirable that the haunch does not show, the haunch is beveled from the tenon to the edge of the rail.
_No.44.A bare-faced tenon_, Fig.