The Collie breed of dog comes in two varieties, differentiated by coat type: rough coat and smooth coat. The rough Collie is familiar to generations of Lassie viewers in the U.S., while the smooth Collie is actually more popular in the United Kingdom. Both types are hardworking, kindhearted and noble, as well as intelligent. They also share the characteristic lean face and wedge-shaped head. The four accepted colors are sable and white, tri-color, blue merle and white. Both types are judged according to the same standards, with the exception of the standards for coat. The head of the Collie breed of dog tends toward the light side relative to the size of the dog. Both in front and profile view, the head resembles a wedge, smooth and clean in outline. On the sides it tapers gradually and smoothly from the ears to the end of the black nose. The end of the Collie's smooth, well-rounded muzzle is blunt but not square. The underjaw is strong and clean-cut. The good-sized teeth meet in a scissors bite. The eyebrows are slightly prominent. The eyes of the Collie breed of dog should be matched in color for most Collies; the exception is blue merles. For all Collies, they are almond-shaped and of medium size. They should have a clear, bright appearance, suggesting intelligence and curiosity. In blue merles, dark brown eyes are preferable, but either or both eyes may be merle or china in color without specific penalty. The Collie's ears are proportionate to the size of the head. "Expression" is said to be a critical component of the Collie breed of dog. While "expression" is difficult to define, it is a combination of the shape and balance of the skull and muzzle, the placement, size, shape and color of the eye, and the position, size and carriage of the ears. The neck of the Collie breed of dog is firm, clean, muscular, and heavily frilled (for both coat types). The neck is fairly long, carried upright with a slight arch at the nape. The Collie's body is likewise firm, hard and muscular, a trifle long in proportion to his height. The ribs are well-rounded behind the well-sloped shoulders and the chest is deep. His back is strong and level, supported by powerful hips and thighs, and the croup is sloped to give a well-rounded finish. The loin is powerful and slightly arched. His forelegs are straight and muscular, with a fair amount of bone considering the size of the dog. The hind legs are less fleshy, muscular at the thighs, very sinewy and the hocks and stifles are well bent. His comparatively small feet are oval in shape. The soles are well padded and tough, and the toes are well arched and close together. The Collie's tail is somewhat long; it is carried low when the dog is quiet, and is carried higher -- although not over the back -- when he is excited. The Collie's gait is smooth and elegant, suggesting both effortless speed and the ability to change direction almost instantaneously. For the rough Collie, his coat is his crowning glory: abundant everywhere except on the head and legs. The straight, harsh outer coat covers a soft, furry and very dense undercoat. His coat is especially abundant on the mane and frill. The face is smooth, the forelegs are smooth (though well feathered to the back of the pasterns), and the hind legs are smooth below the hock joints. The hair on the tail is very profuse. The smooth Collie has a similarly dense undercoat and a short, hard, dense, flat coat. Both types have the same four accepted colors: sable and white, tricolor, blue merle, and white. There is no preference among them.