Branched ends of Reichert’s cartilage in the ear: a histological study using human near-term fetuses

There is little information regarding whether the styloid process “inserts” deeply into the temporal bone petrosa. We examined the involvement of Reichert’s cartilage (RC) in the petrosa using sagittal or horizontal histological sections ofthe heads from 17 near-term fetuses (25-40 weeks). The cranial part of RC usually carried two short branches or protrusions(T-shaped appearance). One of the branches ended in or adjacent to the future tympanic cavity, while another branch endednear the facial nerve canal. Near the latter end, a part of the RC was usually fused with the petrosa, but it was rarely separatedfrom the latter. When a bar toward the tympanic cavity was short or absent, RC displayed a reversed J-shaped course nearthe facial nerve canal and ended at the attachment to the petrosa (3 of 17 specimens). Overall, considerable variations wereevident in the shape, length and topographical relation of RC in the ear. Therefore, an intra-otic root of the styloid process, ifidentified in adults, seemed not to be a simple bar inserting between the tympanic cavity and the vertical portion of the facialnerve canal. Considerable variations in the RC head suggested that the shape was likely to be determined by mechanical loadsfrom the developing petrosa and/or tympanic bone. Those observations were clearly contrast to the degenerating Meckel’scartilage that induces protrusions of the petrosa ant tympanic bone. After birth, endochondral ossification of the petrosaappeared to expand antero-inferiorly to involve all branches of RC.