Which one of the following is not a part of the fallopian tube of the female reproductive system of humans?

The fallopian tube (also known as the oviduct) in the human female reproductive system consists of three main anatomical regions: the infundibulum, the ampulla, and the isthmus. The infundibulum is the funnel-shaped part closest to the ovary; the ampulla is the wider, middle portion where fertilization usually occurs; and the isthmus is the narrow section that joins the uterus.

The endometrium is not a part of the fallopian tube. Instead, it is the innermost mucosal layer that lines the uterus. It plays a crucial role during the menstrual cycle by thickening in preparation for the implantation of an embryo and is shed during menstruation if pregnancy does not occur. Thus, option B is the correct answer.