History of the Great Wall of China the three, China's chief concern since the earliest times had been Mongolia – the home of many of the country's fiercest enemies including the Xiongnu, the Xianbei, the Khitans, and the Mongols. The Gobi Desert, which accounts for two-thirds of Mongolia's area, divided the main northern and southern grazing lands and pushed the pastoral nomads to the fringes of the steppe. On the southern side (Inner Mongolia), this pressure brought the nomads into contact with China. For the most part, barring intermittent passes and valleys (the major one being the corridor through Zhangjiakou and the Juyong Pass), the North China
Gobi jerboa auditory bullae are very large in size, and almost meet at the front of the skull (Smith and Xie 2008). The dental formula of the Gobi jerboa is I 1/1 C 0/0 P 1/1 M 2/2 (R. Taylor). One of the most prominent features of the Gobi jerboa are their ears, since they are almost three times as large as their heads. Their large ears give them an extra keen hearing sense, which helps to serve as extra protection in their vulnerable environment. The great size of their ears also helps to cool their bodies by dissipating heat, since they