Microfil distribution patterns in the head of pigs and Barbados green monkeys. All images are presented in sagittal plane with gradual magnification of the olfactory area adjacent to the cribriform plate. Reference scales are provided either as a ruler in the image (mm) or as a longitudinal bar (1 mm). A-C illustrates images of the pig and D-F images of the monkey. In both species, the Microfil can be viewed in the perineurial spaces of the olfactory nerves external to the cranium, which merge into network of lymphatic vessels in the ethmoid turbinal systems. In A, Microfil can be observed penetrating the dura and entering the cavernous sinus with partial filling of the retromandibular vein (arrow). b – brain; cp – cribriform plate; et – ethmoid turbinates; ob – olfactory bulbs; on – olfactory nerves.