xiphisternum

The xiphisternum (or xiphoid process of the sternum) is at the same level in the axial plane.

This is due to tendinous intersections within the muscle, usually at the level of the umbilicus (belly-button), the xiphisternum, and about halfway between.

Apparent leg length - umbilicus or xiphisternum (noting which is used) to the medial malleolus of ipsilateral leg.

On infants, this may manifest as an apparent 'bubble' under the skin of the belly between the umbilicus and xiphisternum (bottom of the breastbone).