Pneumatic processes in the temporal bone of chimpanzee (Pan troglodytes) and gorilla (Gorilla gorilla)

The ontogeny of human temporal bone pneumatization has been well studied fr om both comparative and clinical perspectives. While a difference in the ex tent of air cell distribution has been noted in our closest living relative s, chimpanzees and gorillas, the processes responsible have been relatively unexplored. To examine these processes, a large, age-graded series of homi noid skulls was radiographed and the progress of pneumatization recorded. A dditionally, a subsample of 30 chimpanzees and 12 gorillas was subjected to high-resolution CT scanning. Neonatal specimens show a well-developed mast oid antrum, as well as a capacious hypotympanum extending into the petrous apex. In African apes, as in humans, the mastoid antrum serves as the focus for air cell expansion into the mastoid and immediately adjacent areas. In chimpanzees and gorillas, however, a pronounced lateral structure, describ ed as the squamous antrum, serves as the focus of pneumatization for anteri or structures such as the squamous and zygomatic. The diminution of this st ructure in Homo sapiens explains the difference in air cell distribution in these regions. (C) 1999 Wiley-Liss, Inc.