The pineal gland contains calcareous particles like grains of sand, and tumours are met with in which similar particles are present. It is necessary, of course, to distinguish these from tumours in which simply a secondary calcareous infiltration has occurred. The psammoraa is composed of soft connective tissue in the midst of which there are calcareous masses in the form of irregular globes, rods, or spines. (See Fig. 90.) The commonest form is the globe, which has rounded projections on its surface like a berry. The origin and significance of these masses is obscure. The tumours are met with in the pineal gland, choroid plexus, and brain substance, and are usually small.' They also occur in the dura mater, where they form half globular tumours, sometimes as large as a cherry and either smooth or irregular on the surface.

The calcareous particles probably arise by deposition around the new-formed vessels. Besides occurring in the simple psammoma, they are met with in sarcomas, myxomas, and other forms of tumour.