Tim, can you give me examples the use of shoulder, knee, and elbow hidden within the 5 element and 12 animal forms?
With arts like Ba Ji and Xin Yi Liu He, the use of those 3 body parts are very obvious in the forms; however, with He Bei and Shan Xi style Xing Yi, I have trouble making them out. Seems to me that both of those styles of Xing Yi rely much more on the fist and palm as striking weapons.

No specific examples, but as an example in general; if you see each technique discretely as, start at A and finish at B, then you may well be unaware/missing oppurtunities over a continuous range A to B, and/or possibly assuming you will be 'allowed' to complete transition A to B 'unchallenged'.

Cherng,
As Chris pointed out, the idea of movements in forms is that the whole body has force throughout, so many movements that "end" a specific way (as a punch for example) will include a flow of force that could be used as many other "techniques" (other strikes, throws...).

There are, however, certain forms that emphasize strikes with the sholder, knee, elbow and head. The Monkey form has several variations of knee techniques, including pulling the opponent into the upward knee, and a jumping forward knee (much like the jumping knee of Thai Boxing). The Water Skimmer form is heavily based on the use of the elbow, as is the Bear form. The Snake Form is used primaily as a throw that uses a shoulder strike to knock the opponent down, and the Swallow Form includes a low leg pick and shoulder strike throw. The primary technique of the Tai Bird is a forward head butt. These are the more obvious techniqes in the animal forms.