The lateral, third, and fourth ventricle choroid plexus of the dog: a structural and ultrastructural study.

The morphology of the choroid plexuses of the lateral, third, and fourth ventricles in dogs was studied by histological and ultrastructural techniques after in situ fixation. Most portions of the plexus in the lateral ventricle showed a parallel arrangement of capillaries, producing a fine corrugation of the overlying layer of epithelial cells. Relatively large amounts of connective tissue separated the capillaries from the epithelium. The fourth ventricle choroid plexus showed short capillary loops projecting into the ventricle and more intimately covered by epithelium. Smaller amounts of connective tissue separated the capillaries from the epithelium. The choroid plexus of the third ventricle showed characteristics seen in the plexuses of both the lateral and fourth ventricles. The total surface of the choroid plexuses in the dog averaged 10.7 cm2, of which 55% was fourth ventricle choroid plexus.