Retraction of scapula at sternoclavicular joint is done by (FMGE Dec 2018)
**Core Concept**
The question is testing the student's understanding of the scapular movement and the muscles involved in its retraction at the sternoclavicular joint.
**Why the Correct Answer is Right**
The retraction of the scapula at the sternoclavicular joint is primarily facilitated by the sternocleidomastoid muscle. This muscle originates from the lateral half of the superior nuchal line of the occipital bone, the posterior part of the superior nuchal line, and the lateral half of the inferior nuchal line, and inserts into the superior surface of the lateral third of the clavicle and the medial third of the sternum. The sternocleidomastoid muscle acts to retract the scapula, which is essential for movements such as adduction and medial rotation of the scapula.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not specify a muscle responsible for retraction of the scapula at the sternoclavicular joint.
* **Option B:** This option is incorrect as it mentions the trapezius muscle, which primarily facilitates elevation, depression, and rotation of the scapula, but not retraction at the sternoclavicular joint.
**Clinical Pearl / High-Yield Fact**
The sternocleidomastoid muscle is a key muscle for movements of the scapula and also plays a crucial role in the rotation of the head and neck.
**Correct Answer: A. Sternocleidomastoid muscle.**