Introduction to Walk Like a Sloth: lessons in ground sloth locomotion
The scapula or shoulder blade is a large, thin, relatively flat bone. Together with the clavicle (collar bone) and sternebrae (breast bones), the scapula is at the center of the sloth’s so-called shoulder girdle, playing an essential role in controlling movement of the upper arm as well as magnifying the arm’s power. The smoother, flatter side is the ventral or “in” side, configured to fit snugly against the ribs on the back. The scapular spine marks the dorsal or “out” side, serving to bring rigidity to this otherwise amazingly thin bone, like the upright part of an “I” beam.