Skeletal muscles come in many shapes and sizes, with each muscle adapted for its position in the body and the job it does.
Quadrate muscles
These are rectangular hard-working muscles. Quadrate muscles are stabilizers along with whatever other function they perform. The rhomboids are a quadrate muscle. While they work to retract the scapula they also stabilize the shoulder blade onto the trunk.
Fusiform muscles
These powerful muscles, such as the biceps, usually bend or straighten a limb. Sometimes, included in the parallel muscle group, these muscles are more spindle-shaped, with the muscle belly being wider than the origin and insertion. Examples are, Biceps Brachii and Psoas major.
Circular muscles
These muscles control body openings, such as the mouth or bladder. These muscles appear circular in shape and are normally sphincter muscles which surround an opening such as the mouth, surrounded by Obicularis Oris and Obicularis Oculi surrounding the eyes.
Triangular muscles
This muscle is narrow at one end and broad at the other. This allows a range of movement, such as at the shoulder.
Strap muscles
These are long muscles that are not especially strong but have good endurance. The infrahyoid muscles, or strap muscles, are a group of four pairs of muscles in the anterior (frontal) part of the neck. The four infrahyoid muscles are: the sternohyoid, sternothyroid, thyrohyoid and omohyoid muscles.
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