The skull is rounded and short in the facial region. The teeth grow throughout life and have cupped grinding surfaces. Nearly all mammals have 7 neck vertebrae, but two-toed sloths usually have 6 or 7, occasionally 8. The ears of Choloepus are inconspicuous, and the eyes are directed forward. The stomach is complex for the digestion of vegetation.
Females have two mammae, located in the chest region.
They sleep with the head raised and placed between the forelegs on the chest. All four feet are often placed so close together that the animal has the appearance of a bunch of dried leaves. They swim voluntarily, using a breast stroke and with the body right side up. When on the ground, where they do come about once a week to urinate and defecate, they have some difficulty standing, but they can rise on the palms and soles and crawl for short distances. Unlike that of most mammals, the body temperature of sloths varies considerably, depending on the temperature of their surroundings.