An ethmoid exposure (os planum) in the orbit of Indri indri (Primates, Lemuriformes).

In 6 of 17 skulls of Indri indri retaining distinct sutures in the medial orbital wall, a small separate bony element intervenes between the frontal and the maxillolacrimal suture. This element is demonstrably continuous with the ethmoid on one such skull. The occurrence of an ethmoid exposure in the orbit of Indri suggests that this trait is not a simple function of orbital size and convergence. Since such an exposure is found in non-cheirogaleine lemuriforms, its distribution provides no support for the hyothesis that lorises and galagos are derived from cheirogaleines.