The magnificent Everprogressing, evercomplex ClaaaaayMan

This is a close-up of some of the more detailed muscles of the spinal erector. You can see the small spinalis cervicis and the bulkier spinalis capitis connecting to the spinal column and back/center of the head on the left. Some of these little muscles were difficult to perceive in harmony, and my first attempt was a mishmash of small chords. After Amy showed me some diagrams and her model, I was able to understand the spirals and curves important to these muscle's relationship with one another. This view illustrates the spiraling nature of the longissimus cervicis and capitus, and the iliocostalis cerivicis  as well as the top portion of the longissimus thoracis. This twisting mass up toward the skull gives us the ability to spin our heads on an axis, but are limited by the flexibility and length. I was having difficulty building these at first, because I didn't have any reference images. Next time I build, I will be sure to have an anatomy book of some sort to refer to the relationships between the muscles, something that is not presented in detail in the muscle atlases we are using. To get the curves and twists, I suggest building onto basic forms while they're on the model with small pieces of clay. Rather than actually trying to twist the muscles or build them with a twist, you can use overlapping and variation of width to suggest a curve or twist. I tried not to get frustrated because I know if I have to do something over again, then it's just giving me a better understanding, and helping me to memorize some of these forms (and maybe even the names.)

I feel my best tool was my hands, rather than cutting out the exact shape, I found it resourceful to smooth and construct the clay with my fingers, using the cutting tools for minor details and connections. Fingers work better than anything for smoothing out the clay. It would be helpful to have a few little tiny ones on my hand for work like this, but evolution has prohibited me.  

Here is a view showing the External obliques, and how they rest on the hip and form is a delicate curve over the gap between the ribs and hips. This muscle was especially hard to build because it is so large, and I wasn't exactly sure how thick it should be from the side. Looking at diagrams however, I think I did a pretty good job, I could use some thinning out in areas along where it attaches to the angle of the rib. This muscle flexes the lumbar toward the front, and also compresses the abdomen. The rectus abdominus were also difficult to build and understand the shape, since they are a bit complex in structure, what with the separations. These are used to compress the abdomen and depress the ribs, similar to the external obliques. The external obliques were frustrating at first, but i used some trimming down to give them shape, and I think they've turned out alright, I'de like to see what Amy has to say. This clay building is a great learning opportunity, as the models will not only be there for reference, but when they are even gone, I hope I can remember these complicated forms for drawing. I have been picturing the obliques especially in my drawings to fill in the curve in the gap between the ribcage and the hips. This process overall is making me more confident and effective in my figure studies and sketches.
The large muscle is the longissimus thoracis, this powerful muscle, along with the triangle shaped iliocostalis lumborum, protect our organs and spine at the gap between the ribcage and hip bones. They also allow us to flex the lumbar vertebrae, and the more limited thorasic vertebrae. 
A miniscule portion of the quadratus lumborum, tucked under the external obliques.  I need to emphasize the two triangles of it, something I didn't pay attention to when building. This muscle laterally flexes and extends the lumbar spine.
Another shot of the external obliques and abdominis as well as the front of the longissimus capitis and iliocostalis cervicis.