Some of the secreted substances are thought to nourish the oocyte and the very early embryo. The muscularis consists of an inner circular muscle layer and an outer longitudinal layer. Peristaltic muscle action seems to be more important for the transport of sperm and oocyte than the action of the cilia. Texts usually refer to four subdivisions of the oviduct. Finger-like extensions of its margins, the fimbriae , are closely applied to the ovary.
Ciliated cells are frequent.
Their cilia beat in the direction of the ampulla of the oviduct. Mucosal folds, or plicae, and secondary folds which arise from the plicae divide the lumen of the ampulla into a very complex shape. Fertilization usually takes place in the ampulla. Mucosal folds are less complex and the muscularis is thick. An inner, longitudinal layer of muscle is present in the isthmus and the last, intramural part of the oviduct, which penetrates the wall of the uterus.