Although the alternative form clearly shows only three strokes, it is still counted as four strokes when using a Chinese dictionary. Compare 氵 from 水 (“water”), 扌 from 手 (“hand”), and 忄 from 心 (“heart”), all of which are a 3-stroke form from a 4-stroke character.
犬 is the 94th radical in the Chinese dictionary. Compound characters such as 狇 mostly use the alternative form at the left of the character. Most represent something to do with dogs or other animals. A smaller proportion (e. g. 狀) use the primary form at the right of the character. A few even show both forms: in 獄 which means "prison" or "litigation"; "words" (言) stand between two dogs to keep them from biting each other.
From Proto-Sino-Tibetan*d-kʷəj-n. This common Sino-Tibetan word has been replaced by 狗 (gǒu) in most dialects except a few Min dialects, such as Fuzhoukēng. In other dialects, this word is mainly found in compounds and not used alone.
From Old Japanese. Derivation uncertain. Various theories exist, including derivation from ancient verb 往ぬ (inu, “to leave, to be gone”), from the way a dog will guard the house while the master is away; from a compound of 家 (ie, “house, home”) + 寝 (nu, “to sleep”, ancient monosyllabic form of modern 寝るneru); from ancient Japanese 狗 (enu, “puppy, dog”), itself of uncertain derivation; or as a borrowing from some other unknown language.