Occurrence of the ventral component of the third branchial nerve as the supernumerary branch of the glossopharyngeal nerve.

The authors found supernumerary branches of the glossopharyngeal nerve in 7 out of 368 head sides (184 bodies) of Japanese individuals. The branches entered the submandibular triangle and connected with the superficial cervical ansa. Teasing revealed that the components of the glossopharyngeal nerve were distributed not only in the subcutaneous layer of the neck but also in the lower facial muscles such as the orbicularis oris. This suggests that the third branchial arch sometimes participates in the formation of the facial muscles which are usually composed of the ventral component of the second branchial arch. Therefore, this supernumerary branch of the glossopharyngeal nerve is probably the ventral component of the third branchial nerve, which is originally distributed in the ventral component of the third branchial arch and usually disappears during later development. The present findings will clearly show how the branchiogenous region is demarcated against the somatic body wall.