Tigris, the second river of western Asia, rises in N. W. Kurdistan, S. of Goljik lake, flows S. S. E. to Diarbekir, thence S. E. to Mosul, and thence S. by E. to its junction with the Euphrates at Korna, where the two form the Shat el-Arab. At its source it is less than 10 m. from the Murad or E. branch of the Euphrates; at Mosul it is about 1G0 m. distant from the sister stream; near Bagdad it is within 20 m. of it, but near Serut the distance has increased to 100 m. Its total course is estimated at 1,150 m., and its width from Mosul to Bagdad, a distance of about 220 m. in a straight line, averages 200 yards; its current in March flows 4¼ m. an hour. The greatest height is attained in the latter part of May, and it resumes its usual level by the middle of June. It is navigable in the flood time between Diarbekir and Mosul for rafts; below Mosul it is navigable for steamers at all seasons. The Tigris is swifter and in the latter part of its course deeper than the Euphrates, and its volume is generally greater. It has been calculated that the quantity of water discharged every second by the Tigris at Bagdad is 164,103 cubic feet. In its upper course it receives from the mountains W. of Lake Van the Bitlis-tchai or Eastern Tigris, which surpasses it in volume of water.

From the Za-gros mountains it receives streamlets which often swell into large rivers. The principal of these are the Upper Zab, the Lower Zab, the Adhem, and the Diyalah. The western affluents are insignificant. The course of the branch streams constantly varies, and some of the tributaries are left dry within a few years of the time that they have been navigable. While the low banks of the Euphrates often cause that river to leave its channel, the Tigris, which runs in a deep bed, seldom varies. (See Euphrates.) - In antiquity the Tigris was the great river of Assyria, and the eastern boundary of Mesopotamia, and on its banks flourished the cities of Nineveh, Seleucia, and Ctesiphon. The name Trigis is supposed to be derived from the old Persian tigra, arrow; its Aramaic name was Digla or Diglath, and the Hebrew Hiddekel.