text: The clavicle of each of these critters has been modified through evolution to suit the critter's particular mode of lifestyle.\n\nThe bat's clavicle is a long, strong bone that articulates with the scapula and the sternum.  It is one of the chief supports of the bat's pectoral girdle, and is important in keeping the thorasic cavity from being crushed when the bat sweeps its wings during flight.  The bat's clavicle is much more mobile than most mammal's, sliding laterally and ventrally during the power stroke of the wing.\n\nThe cat, however, has a very reduced clavicle.  In the felids, the clavicle is barely more than an ossified hunk lodged in the muscle structure of the forelimbs.  This accomodation is due to the narrow and upright stance of the feline body.  It allows for greater freedom of movement, as well as the ability to squeeze through tighter openings than a broad shouldered mammal might be able to.  \n\nThe clavicle of a monkey, or indeed most primates, including humans acts as a strut to stabilize the shoulder joint against the sternum.  This broad shouldered, strong strut support helps increase the strength of arm movements despite the highly flexible and mobile humerus/scapula joint.  This combination of strength and flexibility is what allows primates such as gibbons, chimps, spider monkeys, and to some extent even humans to brachiate, travelling by swinging from branch to branch.  It is also what allows us to throw objects such as rocks, spears, and footballs with both accuracy and power.\n\nThe mole's clavicle is very unusual for a mammal.  It is extremely robust and strong, and articulates directly with the humerus instead of attaching to the scapula.  This helps form an incredibly powerful set of supports for the pectoral girdle and muscles, which moles use for digging deeply and quickly through hardened dirt.