Macroscopic and histologic study to differentiate large glands and bulbi in the perianal body region of the male gray short-tailed opossum, Monodelphis domestica.

On either side of the cloaca of the male Monodelphis domestica, there is a large pack of globular structures lying between the external skin and the ischial arch. The structures within each of these bilateral complexes can be classified into three groups. Group 1 comprises different kinds of glands. There are two large glands, "Paraproctic glands" according to Schaffer (1940), whose spacious cavity is bounded by a secretory epithelium. The secretion is holocrine in a way that cells are shed into the wide cavity. Further, there are two large bodies built of sebaceous acini around a central cavity. The inner surface of the cavity is a squamous stratified epithelium. A peripheral layer of secretory tubuli completes the structure's wall. The bodies are referred to as "Circumanal glands" according to Schaffer (1940). Their excretory ducts end into the cloaca. Group 2 is located between the glands of group 1 and group 3. Macroscopically, the structures of this group are easily mistaken as glands, however, histologically they are identified as a bilateral bulb of the corpus spongiosum, and as a bilateral bulb of the crus of the corpus cavernosum penis. Group 3 includes three different glands that end into a bilateral expansion of the urethra. These accessory genital glands are very distinct due to the histologic characteristics of their secretory epithelium.