The vascularization of the choroid plexus of the lateral ventricle of the turtle (Pseudemys scripta elegans) has been studied by means of vascular corrosion casts and transmission electron microscopy (TEM). A single arterial supply via the choroidal artery and a two-fold venous drainage was found. By its form the plexus was subdivided into two parts: the body, and numerous villi projecting out of the body. The body consists of large convoluted arteries and veins which are covered by a network of vessels always greater than 15 μm in diameter. The villi are composed of a head consisting of vessels with a diameter of 16–50 μm and a stalk represented by one arteriole and one or two veins, which unite at the base of the stalk. An arteriovenous shunt occurs occasionally at the base of the stalk. By their angioarchitecture, six types of villi can be discerned: simple, club-shaped, flat, wrinkled, glomus-like and basket-like villi. Garland vessels were present around arteries only. In ultrathin sections the vessels of the head of a villus possess a thin endothelium with tentacle-like flaps which protrude into the lumen and many pinocytotic vesicles. These vessels were surrounded by a very fragmentary basement membrane and a dense layer of collagen fibrils.
It is suggested that the different areas in the plexus, i.e. the various villi and the body, represent areas with different physiological functions