Figure 3. Delineation of the outer and inner contours (yellow) of (a) an empty and (b) a filled rectum on photos of the male cryo-sections. The caudo-cranial distance between the images is 5.9 cm. For both images, the operator has delineated the inner contours erroneously on purpose, to fix the transversal wall area, A_wall, equal to the mean A_wall of the whole image set of 3.9 cm² (Table 3).