The phrase "comes from sides" can be replaced with a number of synonyms depending on the context. Some possible options include "emerges from both flanks," "originates from opposing edges," "springs up from opposite borders," or "arises from either side." These phrases all convey the idea of something beginning or originating from two distinct locations. Depending on the intended tone or level of formality, other synonyms might include "derives from both margins," "hails from two extremes," or "comes forth from diametrically opposed points." Careful choice of synonyms can add variety and nuance to writing, allowing for more precise expression of meaning.