horse's mane, bristles
騌 centers on the coarse hair along a horse's neck: the mane, and by extension similar stiff bristles.
騌 combines 馬 (horse) with 宗, which likely provides the sound ソウ. The character specifically denotes a horse's mane.
The left side is a horse 馬, and the right side 宗 looks like a roof over a small altar. Picture a horse with a mane so thick it could be a roof over its neck.
For ソウ, imagine sewing a horse's mane: sew -> ソウ, and the bristly mane is being stitched into shape.