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The geographical regions in which Iranian languages were spoken were pushed back in several areas by newly neighbouring languages. Arabic spread into some parts of Western Iran (Khuzestan), and Turkic languages spread through much of Central Asia, displacing various Iranian languages such as Sogdian and Bactrian in parts of what is today Turkmenistan, Uzbekistan and Tajikistan. In Eastern Europe, mostly comprising the territory of modern-day Ukraine, southern European Russia, and parts of the Balkans, the core region of the native Scythians, Sarmatians, and Alans had been decisively been taken over as a result of absorption and assimilation (e.g. Slavicisation) by the various Proto-Slavic population of the region, by the 6th century AD. This resulted in the displacement and extinction of the once predominant Scythian languages of the region. Sogdian's close relative Yaghnobi barely survives in a small area of the Zarafshan valley east of Samarkand, and Saka as Ossetic in the Caucasus, which is the sole remnant of the once predominant Scythian languages in Eastern Europe proper and large parts of the North Caucasus. Various small Iranian languages in the Pamirs survive that are derived from Eastern Iranian.

What is another term for Western Iran?
Answer: Khuzestan
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Garzê Tibetan Autonomous Prefecture and Ngawa Tibetan and Qiang Autonomous Prefecture in western Sichuan are populated by Tibetans and Qiang people. Tibetans speak the Khams and Amdo Tibetan, which are Tibetic languages, as well as various Qiangic languages. The Qiang speak Qiangic languages and often Tibetic languages as well. The Yi people of Liangshan Yi Autonomous Prefecture in southern Sichuan speak the Nuosu language, which is one of the Lolo-Burmese languages; Yi is written using the Yi script, a syllabary standardized in 1974. The Southwest University for Nationalities has one of China's most prominent Tibetology departments, and the Southwest Minorities Publishing House prints literature in minority languages. In the minority inhabited regions of Sichuan, there is bi-lingual signage and public school instruction in non-Mandarin minority languages.

What are the largest minorities of western Sichuan?
Answer: Tibetans and Qiang
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The skeleton consists of very lightweight bones. They have large air-filled cavities (called pneumatic cavities) which connect with the respiratory system. The skull bones in adults are fused and do not show cranial sutures. The orbits are large and separated by a bony septum. The spine has cervical, thoracic, lumbar and caudal regions with the number of cervical (neck) vertebrae highly variable and especially flexible, but movement is reduced in the anterior thoracic vertebrae and absent in the later vertebrae. The last few are fused with the pelvis to form the synsacrum. The ribs are flattened and the sternum is keeled for the attachment of flight muscles except in the flightless bird orders. The forelimbs are modified into wings.

What consists of very lightweight bones?
Answer:
The skeleton