A Bilateral Division of the Parietal Bone in a Chimpanzee; with a Special Reference to the Oblique Sutures in the Parietal

The opening of this paper takes listeners into the quiet corridors of the American Museum of Natural History, where a nine‑year‑old male chimpanzee once famed as a circus attraction rests in skeletal form. Named Chico by his former handlers, his skull bears a startling bilateral split in each parietal bone—an anomaly never before recorded in chimpanzees. The author places this find alongside earlier reports of similar, though less complete, divisions in orangutan crania, setting a comparative stage that hints at deeper developmental patterns across primates.

In clear, methodical prose the study walks through the bone’s architecture: the abnormal sutures run almost parallel to the sagittal line, overlap in a squamous fashion, and cause subtle bends in the surrounding coronal sutures. Measurements of brain capacity and observations of temporal and supra‑orbital ridges flesh out a picture of a largely symmetrical skull that nevertheless challenges traditional ideas of how the parietal region forms. For anyone curious about evolutionary anatomy, the article offers a focused glimpse into the quirks of primate growth.