Viperidae (vipers; order Squamata, suborder Serpentes) A family of compact, sturdy snakes, most of which have a broad triangular head, small, ridged scales, a short tail, and drab coloration. The genus Vipera, with about 15 species, is typical: the moderately large head is broader than the neck, the eyes have vertical pupils, the tail is short and conical, body scales are strongly keeled, the anal shield is undivided, and the subcaudal plates are paired. Many vipers are ovoviviparous (e.g. Vipera ammodytes, horned viper, long-nosed viper, nose-horned viper, or sand viper, V. aspis, asp, aspic viper, or asp viper, and V. berus, adder, common viper, northern viper, or viper). V. berus is unusual in displaying marked sexual dimorphism, the male being more distinctively marked than the female. V. ammodytes, of southern Europe and the Near East, is stockily built and has a protruding horn on the snout. Bitis arietans (puff adder), common in sub-Saharan Africa, feeds on small vertebrates but is highly venomous and dangerous to humans; when provoked it inflates the body and hisses, while preparing to strike. The related B. nasicornis (rhinoceros viper or river-jack) of Central Africa has a pair of large, prominent, horn-like scales above each nostril. Ophiophagous hannah (King Cobra), of India, Malaya, and southern China, the longest of all venomous snakes (sometimes exceeding 5m), was formerly included in the Viperidae; it is now placed in the Elapidae. Viper venom is generally haemotoxic (blood-poisoning) and is injected down hollow fangs, which rotate back against the palate when the mouth is closed. There are about 100 species, occurring in Europe, Asia, and Africa.