The expansion of the allantois also causes a marked reduction in the size of the (1). Although the (2) closes early, the "detached" (1) does not degenerate and disappear; instead, it lies ventral to the embryo as a wrinkled, elongated, tubular sac containing a yellowish-brown fluid. The (1) remains very vascular (vitelline circulation) and continues to play a role in (3); it may also continue contributing to embryonal nutrition by absorbing nutrients from the (4) and transporting them to the embryo via the (5) arteries.