In the female rabbit, the expanded proximal part of the oviduct is known as

The correct answer is uterus.

In the female reproductive system of a rabbit (and many other mammals), the oviduct (fallopian tube) is differentiated into distinct regions. Let's break down the anatomy to understand why the expanded proximal part of the oviduct is referred to as the uterus in this context:
1. Oviduct Structure: The oviduct is a pair of coiled tubes. The anterior-most part of the oviduct opens near the ovary via a funnel-like structure called the fimbriated funnel (or osteum), which helps collect ovulated eggs.
2. Proximal Expansion: Posterior to the narrow tubal part of the oviduct, the tube expands significantly. In rabbits, this expanded, wider proximal portion of each oviduct functions as the uterus (specifically, rabbits have a duplex uterus, consisting of two separate uterine horns or "uteri" opening individually into the vagina).
3. Vagina and Vestibule: Further down, the two uterine horns join to lead into a single median tube called the vagina, which subsequently opens into the vestibule (urinogenital canal).
Therefore, the expanded proximal part of the oviduct where embryonic development occurs is the uterus.