Isthmus

The oviduct is divided into two distinct histological and morphological sections. The isthmus has a more muscular wall, is less winding and a smaller diameter than the ampulla. The ampulla is very tortuous and lined with finger-like projections called fimbria as it opens into the funnel shaped infundibulum at the ovarian end of the oviduct. The junction between the ampulla and isthmus is the site of fertilization. Ciliated epithelial cells, found throughout the oviduct, are important in the movement of eggs and sperm in the oviduct. Muscle contractions are also involved in the movement of eggs and sperm. During estrus, the infundibulum is in apposition to the ovulation fossa. The fimbria on the infundibulum then pick up and direct the egg into the oviduct.