Reproductive tract(Figure 1) The reproductive tract of the mare can be considered as a Y-shaped, tubular organ with a series of constrictions along its length. The outer structures protect the inner, more delicate ones responsible for fertilization and embryo development.
Vulva (Figure 2) The vulva is the external area of the mare's reproductive system, protecting the entrance to the vagina.

Cervix during estrusCervix during diestrus

(Figure 3) The appearance of the cervix as viewed from the top of the vagina during estrus (left) and diestrus (right).

Uterine wall cross-section

(Figure 4) A cross-section through the uterine wall.

Follicular development

(Figure 5) These sections through a mare's ovary illustrate the presence of developing follicles and formation of the corpus luteum (CL), which produces progesterone, a hormone that helps maintain a developing fetus and plays a role in regulating the estrous cycle.