The last part of your shoulder girdle is the humerus (Want to hear a joke about an arm? No. Oh, but it's humerus! Yes, I do indeed enjoy bad jokes), the big solid bone in your upper arm. Tickets to the gun show? The humerus has got 'em. The round head of the humerus articulates with the glenoid fossa on the scapula, mostly held together by tendons - which is why it is so easy to dislocate your shoulder, but you rarely hear about a dislocated hip in the non-geriatric population. Taking a look at all of these tuberosity (more or less a protrusion of bone, something for muscles to hang on to) things we have going on, the infraspinatous and teres minor insert on the greater tuberosity, working to externally rotate the arm. By the way, this is the front view of a left humerus. Just in case you couldn't feel your own trochlea to figure it out...wink. The lesser tuberosity hangs on to the subscapularis muscle and coordinates the internal rotation of the arm.  Then in the groove between the greater and lesser tubercles, the pectoralis major, latissimus dorsi, and teres major attach to contribute to the internal rotation of the arm. One last one! The deltoid muscles gets its very own tuberosity, farther down on the arm. It helps lift your arm up and out laterally.

 

Ok, how about another bad joke to balance out all that terminology? I learned this one in chemistry class. What do we do with people that are sick? We Helium. What if we can't heal them? We Barium.