RESUMEN
We sought a connection between the half-exterior half-interior symptoms (hanpyo hanri sho), mentioned in the classic Chinese Shang han lun text and used in Kampo medicine, and embryology. An agreement between these shao yang (lesser yang) symptoms, and embryonic brachial arch domains was found. A part of the brachial arches strongly agrees with the ruling domain from the trigeminal nerve to the vagal nerve, and a connection was also seen to the vestibulocochlear nerve and partly to the accessory nerve. Thus we believe that half-exterior half-interior symptoms are a condition which relate back to part of the brachial arches, and are a result of so-called Heat reaction. Shang han lun Chinese medicine and embryology are two completely different fields. However, we consider an embryological view of nerve pathways to be helpful in understanding half-exterior half-interior symptoms, at least to a certain degree.