Fig. 1

Frontal schematic representation of a 5-mm human embryo at the fifth week of gestation. Sagittal sections taken through the branchial apparatus demonstrate the anatomic relationship of external clefts and internal pouches as well as the derivation of important head and neck structures. The sixth arch is very small and not visualised as a separate, discrete structure from pouch 4/5 in Fig. 1. [Reproduced with permission from Waldhausen J (2006) Branchial cleft and arch anomalies in children. Seminars in Pediatric Surgery 15:64–69]