Cyclic histological changes of the oviductal-cloacal junction in the viviparous snake Toluca lineata

The structure and seasonal changes of the oviductal‐cloacal junction remain poorly understood in most squamates. This study was undertaken to describe the histology of the oviductal‐cloaca junction of a female viviparous snake Toluca lineata, during gestation, previtellogenesis, and vitellogenesis. The oviductal‐cloacal junction exhibits a wider lumen and thicker layers of connective tissue, smooth muscle layers, and total wall width compared to the posterior vagina. The lining is characterized by thick, short longitudinal mucosal folds. The luminal epithelia differ morphologically from anterior to posterior portions of the oviductal‐cloacal junction. The anterior portion is lined with a simple columnar epithelium composed of nonciliated cells. The middle portion is lined with stratified epithelium that contains an apical columnar cell layer that undergoes morphological changes coincident with the reproductive cycle. The posterior portion is lined with a stratified squamous epithelium. The connective tissue underlying the epithelium contains numerous ovoid cells having abundant acidophilic cytoplasmic granules—eosinophils. Copulation occurs during the previtellogenic stage, as evidenced by the presence of abundant spermatozoa in the lumen of the anterior portion and of a copulatory plug in the middle and posterior portion of the oviductal‐cloacal junction. J. Morphol. 237:91–100, 1998. © 1998 Wiley‐Liss, Inc.