UPDATE: 12/19/13, 5:45 p.m. EST. A joint statement from Patton Boggs and Locke Lord has been added to the third paragraph of this story.

Patton Boggs and Locke Lord have ended discussions about joining forces, and leaders of the two Am Law 100 firms are slated to inform their respective partnerships Thursday afternoon that the negotiations are over, according to a source familiar with the matter.