The structure indicated is the cervical canal.
The uterus consists of a body and a cervix. The cervix forms the neck of the uterus, and communicates inferiorly with the vagina at the external orifice (external os), and superiorly with the uterine cavity via the internal orifice (internal os). The cervical canal is the narrow passage which runs through the cervix.
The inferior part of the cervix bulges into the superior aspect of the vagina and is called the vaginal portion of the cervix (above this is the supravaginal portion). The vaginal part of the cervix is known as the ectocervix.
The endocervix is the name given to the mucosa which lines the cervical canal.
The endocervical mucosa is lined with a single layer of columnar cells, whereas the ectocervix is lined with stratified squamous epithelium. The point where the mucosa of the ectocervix and endocervix meet, is a called the squamocolumnar junction.
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