Going to begin some work on utilizing light and shade to produce some realistic results, but I'd like some opinions on the anatomy beforehand, particularly in reference to the second image.

This was just a very rough approach towards realistic rendering. I gave up midway as there are some issues that I would prefer to consider next time rather than fix up.

This is my current "project". After I am comfortable with the anatomy of this piece I plan to fully render this as smoothly as possible. I would like to achieve a final product close to a renaissance-era painting but considering the digital methods I am using as well as my limited experience I guess it's just me being ambitious, haha.
I would enjoy it if you shared your constructive criticism on both the anatomy of the second image as well as perhaps some on the first, lighting-wise.