Semi-Analytic Models (SAMs) allow one to construct statistical samples of "universes," each populated with numerous galaxies. The dark matter halos and galaxies are constructed through the use of analytic formulas which approximate the relevant physics. This simplistic formulation allows one to vary elements of the physics in order to determine the effects of particular processes on galaxy formation. Currently, SAMs have no accurate method of tracking many galaxy properties (such as size and velocity dispersion) after they experience a merger. Thus, we know little about the theoretical predictions concerning the origin and evolution of the fundamental plane of elliptical galaxies. The fundamental plane is a tight relation between the sizes, masses, and velocity dispersions of ellipticals. However, I have developed a new model for predicting the properties of a merger remnant given the progenitor properties and merger orbit. This model provides a recipe that can be implemented within SAMs to track these quantities. Currently I am working on a project that implements my model within the SAM developed by Rachel Sommerville.