Which component of a casket serves as the horizontal portion where the gasket is placed?

The body ledge flange is the correct choice because it serves as the horizontal component of the casket where the gasket is placed. This flange is crucial in ensuring a proper seal when the casket is closed, as it holds the gasket in place to create an airtight environment. This is particularly important for preservation purposes and for maintaining the dignity of the deceased.

In contrast, the body lining refers to the interior fabric that decorates the inside of the casket, which enhances its aesthetic appeal but does not provide a sealing function. Body panels are the sides of the casket that are visible from the exterior, contributing to its overall structure and design, but again, they do not play a role in sealing. The cap panel generally refers to the top section of the casket as part of its lid, but it is not the segment on which the gasket is positioned. Therefore, the body ledge flange is specifically designed to fulfill the sealing requirement, making it the most relevant component in the context of this question.