Sternocleidomastoid Muscle
This is the large muscle on either side of the neck. This muscle covers and protects many important deeper structures such as the carotid artery and the jugular vein. This muscle starts at the skull just behind the ear (mastoid bone) and travels down to the sternum (breastbone) and clavicles (collarbones).

Thyroid Gland
The thyroid is located at the midline of the neck, under the skin and a few layers of thin muscles. It sits just in front of and to the side of the upper trachea. It secretes thyroid hormone which is important in regulating many functions of the body. The thyroid gland has a right and left lobe which are connected by an isthmus. Learn more about the thyroid.

Parathyroid Glands
These four glands are located just behind the thyroid gland, two on each side. They are critical in helping to regulate levels of calcium in the blood.

Carotid Sheath
This is an envelope of fascia that envelopes three major structures: the carotid artery, internal jugular vein, and vagus nerve.

What is the humerus?

The humerus is your upper arm bone. Other than the bones in your leg, it’s the longest bone in your body. It’s a critical part of your ability to move your arm. Your humerus also supports lots of important muscles, tendons, ligaments and parts of your circulatory system.

If you experience a fractured (broken) humerus, you might need surgery to repair your bone and physical therapy to help you regain your strength and ability to move.

Your humerus — like all bones — can be affected by osteoporosis.

Because your humerus is connected to so many muscles and nerves, injuries to one can often affect the others.

What are your lungs?

Your lungs make up a large part of your respiratory system, which is the network of organs and tissues that allow you to breathe.

You have two lungs, one on each side of your chest, which is also called the thorax. Your thorax is the area of your body between your neck and your abdomen.

Right lung

The lung on your right side is divided into three lobes: the superior, the middle and the inferior. It’s shorter than your left lung, but also wider than your left lung. Both of your lungs are covered with a protective covering called pleural tissue.

Left lung

Your left lung has two lobes: the superior and the interior. Your left lung is smaller than the right because your heart is where the middle lobe on your left lung would be. Your left lung has two parts that your right lung doesn’t have: the cardiac notch (where your heart fits) and the lingula, an extension of the superior lobe.

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