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Gorilla skull. Coloured X-ray of a front view of the skull of a male gorilla (^IGorilla gorilla^i). The gorilla is the largest living primate. Its skull differs from a human skull in that it has more pronounced brow ridges (across centre), a smaller cranial capacity (upper centre), and thus a smaller brain, and a pronounced sagittal crest (top centre). The crest provides an attachment site for the powerful muscles that work the jaws (lower centre). The teeth are used for grinding the vegetation that forms the gorilla's diet. (KEYSTONE/SCIENCE PHOTO LIBRARY/D. ROBERTS/SCIENCE PHOTO LIBRARY)