Something that's described as "deltoid", including your deltoid muscle, is shaped like this
Spread your index and 
middle fingers in a slight V shape, and inject the needle into the middle of that 
V. ... Use your dominant hand (the one that did the injection) to pull back... [DOC] [TLE] Muscular Function and Anatomy of the Arms: Major Muscle Groups ... [PAR] You see, just like the skeletal system is divided into the axial skeleton (that's the 
... muscles of the shoulder that move the upper arm include the deltoid and the ... 
say that this is the muscle that gives your shoulder that rounded shape that it has.