It has two important branches - at the south-west the Gulf of Aden, connecting with the Red Sea through the strait of Bab-elMandeb; and at the north-west the Gulf of Oman, connecting with the Persian Gulf.
In the west and south the principal routes, other than those already mentioned, are from Yambu to Medina, from Jidda to Mecca, Hodeda to Sana, Aden to Sana, and from Mukalla to the Hadramut valley.
As to cost, one transatlantic cable repair cost 75,000; the repair of the Aden-Bombay cable, broken in a depth of 1900 fathoms, was effected with the expenditure of 176 miles of new cable, and after a lapse of 251 days, 103 being spent in actual work, which for the remainder of the time was interrupted by the monsoon; a repair of the Lisbon-Porthcurnow cable, broken in the Bay of Biscay in 2700 fathoms, eleven years after the cable was laid, took 215 days, with an expenditure of 300 miles of cable.
In Arabia progress has been slower, although the surveys carried out by Colonel Wahab in connexion with the boundary determined in the Aden hinterland added more exact geographical Arabia.
The temperatures at the head of the Persian Gulf approximate to those of northern India, and those of Aden to Madras.