The chorionic villi which project into the uterine glands effectively block their openings. Since the glands continue functioning, their ducts become filled with secretion and dilate. These enlarged ducts are referred to as the so-called (1) of the placenta (see Fig. 39). The obstructing chorionic villi absorb the accumulated secretion as (2). Adjacent (1) are separated by endometrial (3) (the maternal blood vessels en route to the syntrophoblast region run in these (3)). The uterine glands, which are greatly enlarged in the placental zone, are separated from the (1) by a layer of condensed connective tissue; this layer is known as the (4).