Development and arrangement of the tympanic plexus and the nerve of the pterygoid canal during the human embryonic and fetal periods.

The constitutional pattern of the n. canalis pterygoidei and the tympanic plexus was studied in a human embryo (SAM 30 mm) and human fetuses (39-71 mm) which were stained according to the Bielschowsky technique. Reconstructions according to the Born technique were made of the fetuses ED and FRA-3. The following was observed during the fetal and embryonic period in the development of the n. canalis pterygoidei: (1) the n. petrosus superficialis major is always a branch of the n. facialis; (2) the n. petrosus profundus major is during the fetal period always a branch of the n. tympanicus and is of considerable diameter; (3) the contribution of the sympathetic branch of the plexus caroticus; (4) an anastomotic branch with the tympanic plexus; (5) the n. sphenoidalis is observed passing from the otic ganglion to the n. canalis pterygoidei during the end stages of the embryonic period (SAM 30 mm). The fibers of this nerve arise from the microganglion which is a detachment from the medial portion of the otic ganglion. Also the following was observed: the anastomosis of the tympanic plexus with the auricular branch of the vagus nerve (Figs. 3(AV) and 4(Av)) and ganglionic accumulations found in relation with these nerves (Figs. 2, 3, 5, 6, 8, 9, 11, 14, 17 and 18).