Amongst the nations under whose dominion it hitherto has remained, the _Baccuris_ are well known, who possess the first territory irrigated by the Arinos; also the _Manbares_, who are wanderers in the land traversed by the river Taburuhina, the first remarkable confluent of the Juruenna on the eastern bank. The _Appiacas_ occupy the centre of the comarca, and have an aldeia with high houses upon the right border of the river Arinos. They are a ferocious people, live by hunting and fishing, and with axes of stone they prepare the timber for the construction of their houses and their canoes. Northward of the last dwell the _Cabahibas_, who speak the same idiom. It is to be hoped that these tribes, when they begin to experience the advantage of iron instruments and clothing, which they can derive alone from the navigators of this river, will become more civilized, and contribute to the cultivation of those neglected districts. The river Arinos, which took the name of a nation at present unknown, rises near the origins of the Paraguay, and falls into the sublime Amazon under the name of the Tapajos. In 1805, Joam Vieges accomplished on this river almost the same voyage as its first discoverer, Captain Joam de Souza e Azevedo; and in 1812, Antonio Thomé de Franca also descended by it, and in the following year proceeded up with his fleet of canoes, laden in the city of Para, being the first individual who performed this voyage, unquestionably less laborious and much shorter than that by the river Madeira. The first considerable river united with the Arinos by the right border is the Rio Preto, which rises between the Paraguay and the Cuiaba, and, by the left, the Sumidor, which originates a little to the north of the Sipotuba. This name is given to it in consequence of disappearing, (after a course of many leagues,) beneath a rock, from whence it issues at no great distance below. A canoe confided to the current at the upper side soon appears at the other. Captain Joam de Souza descended by the Sumidor, and others by the Rio Preto embarking upon it at a situation about ten miles distant from the arraial of Diamantino. It appears singular that none of these navigators descended by the Arinos from its upper part, which, when it receives the Rio Petro, is larger than that river. All the canoes with which those rivers have been navigated were constructed of the trunks of trees produced upon their margins, demonstrating sufficiently the substantial nature of the soil, and its adaptation to all the purposes of agriculture. In twenty-eight hours of navigation, (performed in the course of four days,) from the bar of Rio Preto to that of the Sumidor, Viegas met with nineteen rivers, yet nameless, and almost the whole entered the Arinos by the right. The largest is a few leagues above the mouth of the Sumidor, which latter is little inferior to the Arinos.