Which term refers to the concave curvature of the neck top line that sags toward the ground?

The term that describes the concave curvature of the neck top line, which sags toward the ground, is known as an "Ewe neck." This characteristic is commonly seen in certain dog breeds and indicates a softer, rounded profile in the neck. A ewe neck can affect the overall appearance and structure of the dog, influencing both its movement and performance in various activities.

The other terms do not relate to this specific neck structure. "Frog face" typically refers to a broad, flat facial structure rather than the neck. "Ruff" is used to describe a frill of hair around the neck or collar area, but does not address the neck's shape itself. "Muzzle" refers specifically to the projecting part of a dog's face, encompassing the nose and jaw, which is unrelated to the curvature of the neck. Understanding these distinctions helps highlight why "Ewe neck" is the accurate term for describing this specific neck configuration in dogs.