Endometrial histology in the pigtailed macaque. Photomicrographs of GMA sections showing endometrial histology from pigtailed macaques on day 0,1, 2, 3, 4, 5, 8, and 14 of the artificial menstrual cycle. a-d and i-l show full-thickness sections all at the same magnification (25× original magnification). A line has been drawn to delineate the endometrial-myometrial border. High power photographs of the upper functionalis zone are shown in e-h and m-p (200× original magnification). At the end of the cycle (a, e) the endometrium is thick and the glands are sacculated due to the effect of P. P withdrawal induced endometrial shrinkage (day 1) and the beginning of bleeding by day 2 (note tissue breakdown in (g). The sloughing menstrual surface is clearly evident on d3 and d4 (Arrows in d and i point out menstrual surface). By day 5 the luminal surface is recovered with epithelial cells. During the proliferative phase (d8 and d 14) the endometrium regrows with tubular glands that show abundant mitotic cells (p). Endo = endometrium; Myo = myometrium.