I'm glad to know that the finer points of Chondrichthyian urogenital systems aren't keeping you awake at night.
In sharks in general (the dogfish being a typical shark), the eggs develop in the ovaries, usually only in one ovary. They then are discharged and pass first through the ostia into the oviducts, then through shell glands where sperm are stored and fertilization occurs before moving on through the oviducts to the uteri, where the embryos develop. The ostia fuse in the falciform ligament, which attaches the liver to the abdominal wall and is not directly involved in reproduction. The ostia are merely the openings to the oviducts; no development occurs there. In sharks they are enlarged to accommodate large eggs. How exactly do the eggs get from the ovary to the ostia? I guess they ask directions.