page_title: Oviduct
section_title: Amniotes
hierarchical_section_title: Oviduct / Amniotes
caption_attribution_description: English: Oviduct of a laying hen 1 Infundibulum, 2 Magnum, 3 Isthmus, 4 Uterus, 5 Vagina with egg inside
context_page_description: The passageway from the ovaries to the outside of the body is known as the oviduct. In female mammals this passageway is also known as the uterine tube or Fallopian tube. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body. Normally, these are paired structures, but in birds and some cartilaginous fishes, one or the other side fails to develop, and only one functional oviduct is found.
  Except in teleosts, the oviduct is not directly in contact with the ovary. Instead, the most anterior portion ends in a funnel-shaped structure called the infundibulum, which collects eggs as they are released by the ovary into the body cavity.
  The only female vertebrates to lack oviducts are the jawless fishes. In these species, the single fused ovary releases eggs directly into the body cavity. The fish eventually extrudes the eggs through small genital pore towards the rear of the body.
context_section_description: In amniotes – reptiles, birds, and mammals – the egg is enclosed with an outer layer, or amnion, which has led to further development of the oviduct. In reptiles, birds, and monotremes, the main part of the oviduct is a muscular tube, capable of considerable distension to transport the large eggs that are produced. This part of the oviduct is lined with glands that secrete the components of the egg white. The lower portion of the oviduct, or uterus, has a thicker layer of smooth muscle and contains the glands that secrete the egg shell. 
  In marsupials and placental mammals, the uterus becomes lined by an endometrium, and is more developed than in egg-laying amniotes. In many placental mammals, the uteri of each side become partially or wholly fused into a single organ, although in marsupials they remain completely separate. In mammals, the portion of the oviduct above the uterus is referred to as the Fallopian tube.
  For birds, the oviduct is composed of:
  Infundibulum (formation of Chalazae, place of fertilisation)
  Magnum (formation of egg white)
  Isthmus (formation of the shell membrane)
  Shell gland (formation of egg shell)
  Vaginal homologue (formation of cuticula)
  (See matching numbers in the picture)
caption: Oviduct of a laying hen
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