The robe is of a very dark brown, which seems black against the snow, and the hair all over the body is coarse and long, reaching down below the belly to the knees (especially long on the rump, where I measured some that was fifteen to twenty inches), and under the throat it hangs down as a thick mane. There appears to be a decided tendency to a hump, which is emphasized by the shorter stiffish hair that covers shoulders and the base of the neck. And there is a saddle mark of a dirty grayish white. Underneath this hair and over all the body grows a coat of mouse gray wool of fine texture, which protects the animal in winter and is shed in the summer. No wool grows on the legs, which are massive, and although short, appear to be shorter than they are because of the long hair that falls over them. In running, they have a rolling, choppy kind of a gait, and I noticed when they fell from a rifle wound they could not get on their feet again.
The growth of the horn is very interesting. It begins exactly as with domestic cattle by a straight shoot out from the head. For the first year, it is impossible to tell the difference between the sexes by the horns. In the second year, the bull horn is a little whiter than that of the cow; the forehead of a two-year musk-ox I killed showed a forehead covered with short, curlish hair. In this year the cow’s horn begins to show a downward turn, and is fully developed at its third year. The bull’s horns, on the contrary, are just beginning to spread at the base in the third year. They continue spreading toward the centre of the forehead until they meet in the bull’s fifth year, but in the sixth year they begin to separate, leaving a crevice in the centre which widens as the bull ages until it is from an inch to an inch and a half wide. In the cow these crevices also open by age to even a greater extent than in the bull. The horns of both bull and cow darken as they reach their full development, until they are quite dark from six to eight inches toward the base; and as the animal ages the extreme darkness of horn disappears, until finally in the old animal of either sex there remains only a black tip about a couple of inches on the very point of the horn. As the crevice between the horns in both sexes widens, the base of the boss on each side thickens to at least three inches in the bull and two or less in the cow. On the boss the horn is corrugated, but at the turn it becomes smooth, and is polished like an ox horn on the point.