At the basis of the social structure stand the trinity of Kami, mythologically called the Central Master (Naka-Nushi) and the two Constructive Chiefs (Musubi no Kami). The Central Master was the progenitor of the Imperial family; the Constructive Chiefs were the nobility, the official class. What was originally involved in the conception of official functions, we learn from incidents prefatory to the expedition conducted by Ninigi for the subjugation of Japan. Amaterasu (the Sun goddess) attached to the person of her grandson four chiefs and one chieftainess. To two of the former (Koyane and Futodama) she entrusted all matters relating to religious rites, and they became respectively the ancestors of the Nakatomi and the Imibe families. To the female Kami (Usume) was entrusted the making of sacred music and she founded the Sarume family. Finally, all military functions were committed to the chiefs, Oshihi and Kume, whose descendants constituted the Otomo and Kume families. In every case these offices were hereditary for all time, and the families of their holders constitute the aristocracy of the nation, marrying among themselves and filling the highest offices from generation to generation. Their members bore the title of hiko (son of the Sun) and hime (daughter of the Sun), and those that governed towns and villages were called tomo no miyatsuko, while those that held provincial domains were entitled kuni no miyatsuko. This was the origin of the Japanese polity. The descendants of Amaterasu, herself a descendant of the Central Master, occupied the throne in unbroken succession, and the descendants of the two Constructive Chiefs served as councillors, ministers, and generals. But the lineage of all being traceable to three chiefs who originally occupied places of almost equal elevation, they were united by a bond of the most durable nature. At the same time it appears that this equality had its disadvantage; it disposed the members of the aristocratic families to usurp the administrative power while recognizing its source, the Throne, and it encouraged factional dissensions, which sometimes resulted disastrously. As to the middle and lower classes, no evidence bearing on their exact composition is forthcoming. It is plain, however, that they accepted a subordinate position without active protest, for nothing like a revolt on their part is alluded to, directly or indirectly, in the Records or the Chronicles. The term for all subjects was tomobe. DWELLING-HOUSES