The Triangular bone, also known as the Triangular scapula or the Os scapulae, is one of the bones in the human shoulder. It is a flat, triangular-shaped bone that lies on the posterior aspect of the thorax, between the second and seventh ribs. The bone is positioned in such a way that it forms the posterior part of the shoulder girdle.

Function:

The Triangular bone serves as an attachment site for many important muscles, such as the trapezius, rhomboids, and serratus anterior muscles. These muscles are responsible for the movement and stabilization of the shoulder joint.

Location:

The Triangular bone is located on the posterior side of the thorax, between the second and seventh ribs.

Relation with other bones:

The Triangular bone is located between the clavicle and the humerus bones. It also articulates with the acromion process of the scapula bone.

Conclusion:

In conclusion, the Triangular bone is a flat, triangular-shaped bone located on the posterior aspect of the thorax, between the second and seventh ribs. It serves as an attachment site for many important muscles and is an important component of the shoulder girdle. Therefore, the correct answer to the given question is option 'D' - Scapula.

Scapula (shoulder blade) is the largest of the bones that make up each half of the pectoral (shoulder) girdle. It is a flat triangular bone, providing anchorage for the muscles of the forelimb and articulation for the humerus at the glenoid cavity. It is joined to the clavicle (collar bone) in front. The clavicle is a bone that forms part of the pectoral (shoulder) girdle, linking the scapula (shoulder blade) to the sternum (breast bone). In humans, it forms the collar bone and serves as a brace for the shoulders.