Gnolls are a weird D&D monster — hyena-headed humanoids. The name is taken from Lord Dunsany, as the original edition of D&D mentions (“Lord Sunsany….”) in the brief description of gnolls. Lord Dunsany does not describe his gnolls* in any detail, and the first edition description just suggests they may be a hybrid of gnomes and trolls. But the look of the AD&D monster is pure Medievalism — they are the Cynocephalies (Dog-headed people) of Medieval folklore.
Strangely, in some traditions St. Christopher is depicted as a dog-head too.
I don’t know why one is a lefty and one is a righty.
*Dunsany actually used the spelling “gnoles” in his story “How Nuth would have practised his art upon the gnoles,” which is collected in his The book of Wonder (the link goes to a free pdf). Because of this spelling, I would later confound that story with the story “The man who sold rope to the gnoles” by Margaret St. Clair and for a while I thought Dunsany wrote that one too. St. Clair gives a much more alien appearance to gnoles, which are not described in much detail apart from the fact that they have tentacled faces and use gems for their eyes. The rope salesman makes a major faux pas regarding this last fact.