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Most muscles on the body are **parallel** in structure. Parallel muscles are long and run parallel to the length of the muscle. They are capable of exerting a strong force over a relatively small range of motion.
Examples of parallel muscles in the body include the rectus abdominis (the "abs") and the sartorius muscle in the thigh. These muscles are well-suited for tasks that require strength and endurance over a limited range of motion, such as maintaining posture.
Muscles that are **fusiform** are another common muscle type found in the body. Fusiform muscles are spindle-shaped with a wider belly that tapers at the ends. They are efficient for generating a wide range of motion but may not be as strong as parallel muscles.
In contrast, **pennate** muscles have fibers that attach obliquely to a tendon running through the muscle. This arrangement allows them to generate more force but with a smaller range of motion. Examples of pennate muscles include the deltoid muscle in the shoulder.
Circular muscles, also known as **circular** or **sphincter muscles**, are found in structures like the eye (for controlling pupil size) and the digestive system (for controlling the opening and closing of passages). They form rings around an opening and are responsible for constricting or dilating that opening.
In summary, most muscles in the body are parallel in structure, while there are also fusiform, pennate, and circular muscles serving specific functions in different parts of the body.
