A Cross Section of the Terminal Gut

Comparing backward along anatomical specimens of the bare-nosed wombat, the intestinal contents are at first yellow-green, resembling a thick slurry; farther back, the color is darker and the texture harder. It does not enter the gut already carrying clear boundary lines. The edges are concentrated in roughly the final seventeen percent of the intestine. Cut across that region, and the intestine that had extended along its length leaves only a section: the contents in the center, surrounded by a ring of intestinal wall of uneven thickness. When this ring of intestinal wall later enters the model, the stiffer regions contract more quickly, while motion at the centers of the softer regions is relatively slower; yet the section before the eye does not yet contain this difference in speed, only one segment thicker and another thinner, alternating around the circumference.

Some regions are close to twice as thick as others. The researchers removed tissue from different positions and measured it in tension; the stiffness measured in the thicker regions was about four times that of the other regions. Thickness can be seen directly at the cut edge, but stiffness appears only after the tissue is subjected to force: the difference within the same ring of intestinal wall remains partly in the section and partly hidden in the ease or difficulty of deformation. From this section alone, the edges still seem like a static result. Following the measurements, the model alternately arranges softer and stiffer regions into a two-dimensional elastic ring; the thicknesses on the dissection table thereby acquire another observable state—contraction.

The model makes this ring undergo a series of circumferential contractions. Stiffness does not become an immobile boundary in the model, nor does softness yield uniformly; they still belong to the same circumference, yet different places do not change contour at the same speed. This difference is not expanded into the origin story of a complete object, nor does it need to borrow another shape to explain itself. The ring continues to contract, and angles appear in the contour.