Final answer:
The manubrium is the wider, superior portion of the sternum that has a shallow, U-shaped border called the jugular notch where the clavicles articulate. The clavicular notch is the site of the sternoclavicular joint. The correct option is a,
Step-by-step explanation:
The sternum is the elongated bony structure that anchors the anterior thoracic cage. It consists of three parts: the manubrium, body, and xiphoid process. The manubrium is the wider, superior portion of the sternum. The top of the manubrium has a shallow, U-shaped border called the jugular (suprasternal) notch.
This can be easily felt at the anterior base of the neck, between the medial ends of the clavicles. The clavicular notch is the shallow depression located on either side at the superior-lateral margins of the manubrium. This is the site of the sternoclavicular joint, between the sternum and clavicle. The first ribs also attach to the manubrium.
Therefore, the correct option is a.