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 of the 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 ended near the facial nerve canal. Near the latter end, a part of the RC was usually fused with the petrosa, but it was rarely separated from the latter. When a bar toward the tympanic cavity was short or absent, RC displayed a reversed J-shaped course near the facial nerve canal and ended at the attachment to the petrosa (3 of 17 specimens). Overall, considerable variations were evident in the shape, length and topographical relation of RC in the ear. Therefore, an intra-otic root of the styloid process, if identified in adults, seemed not to be a simple bar inserting between the tympanic cavity and the vertical portion of the facial nerve canal. Considerable variations in the RC head suggested that the shape was likely to be determined by mechanical loads from the developing petrosa and/or tympanic bone. Those observations were clearly contrast to the degenerating Meckel's cartilage that induces protrusions of the petrosa ant tympanic bone. After birth, endochondral ossification of the petrosa appeared to expand antero-inferiorly to involve all branches of RC.