The orbital mosaic in prosimians and the use of variable traits in systematics.

Study of 579 skulls, representing all 33 extant prosimian species and several anthropoids, shows that an orbital exposure of the ethmoid occurs in most Malagasy genera. A palatine-lacrimal contact is normal only in Lemur; the zygomatic-lacrimal contact occurs in most lorisiform species. Lepilemur shows possibly significant resemblances to lorisiforms. The vomer appears in the orbit of some ceboids. Cebids are distinguished by a canal running from the orbital apex through the basicranium. It is argued that skull shape and jaw musculature affect the size and shape of certain orbital-mosaic components. Frequencies of traits, rather than typologically 'normal' traits, may be taken as synpomorphies linking different species cladistically.