鸟是两足、恒温、卵生的脊椎动物,身体呈流线型(纺锤型),体表覆有羽毛,一般后肢能行走前肢变成翼(有的种类翼退化),大多数能飞;它们胸肌发达,直肠短,食量大消化快,即消化系统发达,有助于减轻体重,利于飞行;心脏有两心房和两心室,心搏次数快;体温恒定;呼吸器官除肺外,还有由肺壁凸出而形成的气囊,用来帮助肺进行双重呼吸。 Birds are two-legged, thermostatic, oviparous vertebrates that are streamlined (spindle-shaped) with body covered with feathers. The hindlimbs are generally able to move their forelimbs to wings (some species are wing degenerated) and most fly; their pectoralis muscular Short rectum, large appetite digestion fast, that is, the digestive system developed to help reduce weight, conducive to flight; the heart has two atria and two ventricles, fast heartbeat times; body temperature constant; respiratory organs in addition to the lungs, Protruding and formed balloon, used to help the lungs to double breathing.