蛇 Snake

蛇（学名：Serpentes），是無足的爬蟲類動物的總稱，属于爬行纲有鳞目蛇亚目的总称。又有虵、虺、螣、蚦、蜧、蜦、长虫等別稱，根據品種也會有蝮、蚺、蟒、蝰等近義稱呼。正如所有爬蟲類一樣，蛇類全身佈滿鱗片。所有蛇類都是肉食性動物。目前全球共有3,000多種蛇類，包括體型最短小的細盲蛇科以至最長的蟒科及蚺科。為了配合蛇類窄長的身體，成對的內臟（如肺、腎）會在蛇體前後排列，而非左右互對。

部分蛇類擁有毒性，能令被其咬擊的生物受傷、疼痛以至死亡。蛇的另一個特徵是顎部能作出廣角度的開合，因此能吞食比自己身型龐大的獵物。生物研究指蛇類大概於白堊紀時代由蜥蜴類衍生而成。現代蛇類的分類研究，大概可追溯至古新世時代。目前紀錄中最巨型的蛇類是活於古新世的泰坦巨蟒，長度達13米長，其化石被發現的年份是2009年；^[1]目前體型最細小的蛇類是卡拉細盲蛇，長度約只有10公分長而已。^[2]

Snakes are elongated, legless, carnivorous reptiles of the suborder Serpentes^[2] that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads with their highly mobile jaws. To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most have only one functional lung. Some species retain a pelvic girdle with a pair ofvestigial claws on either side of the cloaca.

Living snakes are found on every continent except Antarctica, and on most smaller land masses — exceptions include some large islands, such as Ireland and New Zealand, and many small islands of the Atlantic and central Pacific.^[3] Additionally, sea snakes are widespread throughout the Indian and Pacific Oceans. More than 20families are currently recognized, comprising about 500 genera and about 3,400 species.^[4][5] They range in size from the tiny, 10 cm-long thread snake to the reticulated python of up to 6.95 meters (22.8 ft) in length.^[6] The fossil species Titanoboa cerrejonensis was 13 meters (43 ft) long.^[7] Snakes are thought to have evolved from either burrowing or aquatic lizards, perhaps during the Jurassic period, with the earliest known fossils dating to between 143 and 167 Ma ago.^[8] The diversity of modern snakes appeared during the Paleocene period (c 66 to 56 Ma ago). The oldest preserved descriptions of snakes can be found in the Brooklyn Papyrus.

Most species are nonvenomous and those that have venom use it primarily to kill and subdue prey rather than for self-defense. Some possess venom potent enough to cause painful injury or death to humans. Nonvenomous snakes either swallow prey alive or kill by constriction.