I happened to stumble across a heap of images which I hope will help the novice/beginner archer, and maybe reinforce what a great many of us already know. The images are from a page aimed @ African game as you will see in the watermarks and URL's but there are some species that we have here. If anyone has any more of similar quality feel free to add any to this post.
Firstly is a very basic image that shows entry/exit angles, it is not of the african game forum but another picture i stumbled across.
Drawing a line from the rearward end of the scapula to the elbow joint is what most hunters would consider the "triangle".
Hope it helps the new and old alike.