The occurrence of residual cartilage or defective ossification in certain parts of the petrous bone in late fetal life or in early childhood has been recognized for some time. In the region of the fissula ante fenestram this defective development was found by Bast,1 Anson and Wilson,2 Anson and Martin3 and Wilson4 to occur in a large percentage of fetuses and young children. They suggested that this unstable condition in the region of the fissula ante fenestram may be one of the factors which initiate a late attempt at rebuilding of bone and which may result in sclerotic bone. Since otosclerotic bone usually occurs in this region and replaces the residual cartilages, the interpretation sounds plausible.
Another place where such residual cartilages occasionally occur is the region of the "fossula post fenestram." Bast5 showed that residual cartilage or defective ossification in this location is rare and found it in only
BAST TH. DEVELOPMENT OF THE OTIC CAPSULE: V. RESIDUAL CARTILAGES AND DEFECTIVE OSSIFICATION AND THEIR RELATION TO OTOSCLEROTIC FOCI. Arch Otolaryngol. 1940;32(4):771–782. doi:https://doi.org/10.1001/archotol.1940.00660020776009
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