The sacral foramina.
The sacral foramina, particularly the first three, are not simple fenestrations. Each foramen is a Y-shaped complex of canals, all with indefinite margins. The complexes lie obliquely at approximately 45 degrees to the coronal plane. An appreciation of these facts facilitates the recognition of the anatomy of plain films, tomographs, and computerized scans.
D050723:Fractures, Bone / Q000000981:diagnostic imaging; D006801:Humans; D012447:Sacrum / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000293:injuries; D014056:Tomography, X-Ray; D014057:Tomography, X-Ray Computed; D014948:Wounds, Gunshot / Q000000981:diagnostic imaging