THYMIC VASCULAR SYSTEM OF THE EUROPEAN COMMON FROG, RANA-TEMPORARIA -A SCANNING ELECTRON-MICROSCOPIC STUDY OF VASCULAR CASTS

Vascular corrosion casts of the thymus of adult individuals of the Eur opean common frog, Rana temporaria, were analysed by scanning electron microscopy. The main arterial vessel, which is derived either from th e temporal artery or from the auricular ramus, approaches the central territory of the gland and branches into ''twigs'' that, on penetratin g the parenchyma, give rise to capillaries. Most of these capillaries run vertically towards the surface of the gland; they either join the super ficial capillary plexus or follow this plexus for a variable dis tance and then run back towards the medulla, forming capillary loops. The former capillaries link with the extensive venous plexus composed of irregular meshes, whereas the latter capillaries join the venules a t the cortico-medullary boundary and finally escape into collecting ve ins on the gland surface. The venous twigs, which join together near t he gland, form the main thymic vein, which empties into the external j ugular vein. The details of the thymic vasculature of the anuran amphi bian, R.temporaria, are compared with those described in mammalian spe cies, viz. the mouse, rat and guinea pig.