Final answer:
The statement is true; the deltoid is a large, triangular-shaped muscle that creates the rounded contour of the shoulder and is responsible for various arm movements.
Step-by-step explanation:
The statement that "the attachments of the deltoid form a fan-shaped muscle responsible for the rounded contour of the shoulder" is true. The deltoid is a large, triangular-shaped muscle that covers the shoulder, providing its rounded shape and contour. Named for its resemblance to the Greek letter delta, which is triangular in shape, the deltoid muscle plays a critical role as the major abductor of the arm.
Additionally, it also facilitates flexing, medial rotation, extension, and lateral rotation of the arm. The muscle originates on the clavicle and scapula and inserts into the humerus (arm bone), with its tendons forming part of the rotator cuff, which is crucial for the stability of the shoulder joint along with other muscles such as the subscapularis, supraspinatus, infraspinatus, and teres minor.