Summary of embryologic steps of the stapedial and ophthalmic systems
| Stapedial System | Embryo Size (mm) | Ophthalmic System |
|---|---|---|
| Regression of the second aortic arch; hyoid artery formation (dorsal remnant of the second aortic arch) | 4–5 | Primitive maxillary artery as temporary branch; primitive dorsal OA appearance |
| Elongation of the hyoid artery; annexation of the mandibular artery (first aortic arch) by the hyoid artery (second aortic arch) | 5–6 | Primitive hyaloid artery = plexiform channels; primitive ventral OA appearance |
| Cranial growing of the hyoid artery (SA) passing into the middle ear (crus of the stapes) | 7–14 | Formation of primitive hyaloid and common ciliary arteries |
| Maximum development of the SA; extension of the 2 branches of the SA, supraorbital and maxillomandibular | 16–19 | Migration in origin of the primitive ventral OA; regression of the primitive dorsal OA; formation of the anastomotic ring |
| Regression of the transosseous (superior orbital fissure) segment of the supraorbital branch | 20–24 | Ventral interruption of the anastomotic ring; annexation of the supraorbital branch by the OA |