The next few stages are checking and rechecking measurements. Only when we have all of the elements in the first phase down - however general they may be - can we see what needs to be corrected. There are many out there who try and get the whole thing right on the first pass, going from area to area, finishing as they go. I've seen good paintings happen that way, but personally I can't make heads or tails of it. I think I can attribute it to studying so long with a sculptor - in three dimensions you must work on the whole piece at once if you want to make it read properly.
In any case, the first set of adjustments I want to make are the bigger ones. The cranium is the largest part of the head, so I started with that. If that is in place, and the cheekbones are also set, then the eye sockets can be imagined. Patmore was 73 when he died, so his sockets are fairly clear even with skin draped over them, but with most sitters, the sockets will have to be imagined. One thing that is poorly represented here in terms of good practice are the eyes. Typically I'd recommend placing an orb in each socket and leaving it at that until a bit further down the line. Eyelids are such a thin layer of skin that for form's sake they just aren't necessary to place on the eye at this point. If you have the sockets and the eyeballs, then that is all you really need. Your drawing will look a bit disturbing for a while, but that's okay. I even put in eyebrows - if I saw one of my students add in the eyebrows this early on, I might just grab some clippers and shave his or her eyebrows off. In other words, focus on the sockets, NOT on the eyebrows or lids.
The nose was developed - I estimated the width of the nostrils, knowing that I will likely need to adjust that measurement down the line, but I wanted to eyeball it first. As with everything else, the most educated changes can only be made once everything is in place. Only then can you see what is painfully incorrect. The width of his mouth is established, along with the height of his lips. This was also estimated. I placed a bit of flesh hanging off of his jaw, as his jowls are a fairly prominent feature.
I am constantly rechecking the vertical axis quarters that were established in phase one, and seeing more specifically where the features fall on them. In elaborating on the features, I try and keep the major shapes in mind before any sort of specifics are laid in. Think of the barrel of the mouth rather than the lip lines. Think of the front, sides and bottom of the nose rather than the nostrils. If you are going to be be picky about anything in this stage, at least let it be the bony landmarks - the areas where the skin is the thinnest and the skull is clear, such as the nasal bone, cheekbones and the top of the skull. Make sure your centerline is traveling over all of the features like a topographical map, as it will make your mistakes clear and easy to fix.
Regarding 'contours' - this is a touchy subject. Contours are a handy tool to use for measurements and alignment, but you must never forget that in life, they do not exist. Every object is a form in space, not lines. If you think in terms of contour lines, you are already flattening your drawing. In that respect, they are toxic. Use them as a tool, but you must think around your subject at all times. For example, the contour of Patmore's face on the left is mirrored within his face on the right. That is a hard thing to explain in a blog, and if it doesn't make sense, just remember the part where I said contours are poison and run with it.