Fig. 1.

Frontal view of the orientation of the limbs in relation to the thorax in Choloepus didactylus reconstructed after x-ray images. Dotted lines represent primary muscles of the ‘muscular sling’ in the pectoral girdle of a generalized pronograde therian mammal. Only the first thoracic vertebra, rib, and the frontal part of the manubrium sterni are shown. There are no articulating surfaces in the sternoclavicular joint (see text). M. serratus ventralis and m. rhomboideus are unsuited to suspend the thorax between the limbs of C. didactylus.