Development of glossopharyngeal nerve branches in the early chick embryo with special reference to morphology of the Jacobson's anastomosis.

The development of glossopharyngeal nerve branches was studied by an immunohistochemical technique which stains the whole nervous system in situ. Prior to the formation of the ramus (r.) lingualis IX, pre- and post-trematic branches developed just beneath the pharyngeal ectoderm. This mode of development resembled that of the chorda tympani. The post-trematic nerve seemed to be a precursor of the r. lingual. IX. In addition to the r. pharyngeus dorsalis IX, another branch, r. pharyng. posterior IX, appeared. Both these branches formed an anastomosis with the facial and vagus beneath the dorsal aorta. The term Jacobson's anastomosis seemed to be most suitable to refer to an anastomosis made up of these dorsal pharyngeal branches of cranial nerves VII, IX and X. The primary anastomosis between the facial and the glossopharyngeal nerves in the chick is only temporarily present and is comparable to the similar anastomosis in a shark in which the sympathetic system is not present in the cranial region.