Its actually about the size and shape of an almond. That is where the word comes from, Amygdala is greek for almond. Many brain areas got their name from early anatomists who would probe the structure without any clue as to what was what, what did what, and what what was connected to, etc. They simply looked at the crude organization and named structures after the things they looked like. Another famous example is the hippocampus, which looks like a seahorse and, infact means seahorse, again in greek I think, or Latin, those are usually the two languages they used to name these things.