Vertebrates with short period of pregnancy, the marsupials tend to have small and dependent younglitters. The period of pregnancy varies of 14-15 days and, the younglitters finish his development in the pouch, being this period, considered as an external gestation by some authors. The mammary gland is located internally to the pouch, in number of 11 the papilae which were connected to the younglitters come more developed, in lenght. In the microscopic analysis, the mammary gland of the opossum resembles each other to the one of the domestic mammals, except for the absence of the muscle sphincter papillae.
Opossum; mammary gland; papillae
