The naming of the approximately 700 muscles in the human body is based on a set of criteria designed to provide descriptive information about each muscle, making it easier to identify and remember them.

The key factors used in naming muscles include:

1. Region of the Body: Certain muscles in the body are classified based on their location or association with a specific area. For example, the temporalis muscle is in the head region, whereas the brachialis is in the arm.
2. Position and Depth: Muscles visible on the body's surface are often termed 'externus' or 'superficialis', while deeper muscles are referred to as 'internus' or 'profundus'. Muscles that position or stabilize an organ are called 'extrinsic', while those located entirely within an organ are 'intrinsic'.
3. Direction: Some muscles are named according to the direction in which they run relative to the body's longitudinal axis. 'Transversus' refers to muscles running across this axis, while 'oblique' denotes muscles running at a slanting angle.
4. Fascicle Arrangement: The term 'rectus' is used for muscles with straight fascicles running along their longitudinal axis. For example, 'rectus abdominis' refers to a muscle in the abdomen with straight fascicles.
5. Structural Characteristics: Some muscles are named after their distinctive structural features, such as the number of tendons of origin, shape, and size. For example, 'biceps brachii' has two tendons of origin, 'trapezius' is trapezoid-shaped, and 'longus' refers to long muscles.
6. Origin and Insertion: Many muscle names indicate the specific origin and insertion points. For example, the 'genioglossus' originates at the chin or 'geneion' and inserts in the tongue or 'glossus'.
7. Action: Many muscles are named after their primary function or action, such as flexor, extensor, pronator, abductor, adductor, and rotator.
8. Particular Occupations or Habits: A few muscles carry names related to specific movements associated with certain occupations or habits. For instance, the 'buccinator' compresses the cheeks as if blowing a trumpet, and the 'sartorius', the longest muscle in the body, is active when crossing legs, reminiscent of a tailor's sitting position.