THE PLATYSMA MUSCLE 

When your collar is too tight it is the constriction of the platysma muscle that helps loosen it. Otherwise this muscle doesn’t have much function. Laxness of this muscle is often a major factor in causing the sag under the chin in older people (this is not just aging skin, or from accumulating fat). This muscle forms the outermost layer of the neck muscles.  It is a broad, thin muscle.

THE SCALENUS MUSCLE

The scalenus muscle helps lift the ribcage, assisting in breathing. It also assists in some rotation of the neck and flexion of the upper spinal column. Whereas the longus colli and the longus capitis muscles course upward, the scalenus muscle courses downward. Muscles always shorten in the direction of their origin.

THE STERNOCLEIDOMASTOID MUSCLE

The sternocleidomastoid muscle aids in rotating the head and neck and in lowering the chin to each side. It also assists breathing by lifting the sternum when you inhale. It arises in two places—on the top of the manibrium of the sternum and on the clavicle. 

THE SKULL, NECK, AND UPPER BACK: POSTERIOR VIEW

In this illustration you see the skull, seven cervical vertebrae, and eleven of the twelve thoracic vertebrae with ribs attached, from the back or posterior view. The scapula, a bit of the clavicle, and the top of the humerus can also be seen.

THE BONES OF THE NECK: INTERIOR-ANTERIOR VIEW

Here you see the seven cervical vertebrae along with the next three thoracic vertebrae, a section of the skull showing the mastoid process, and two ribs, all seen from the ventral (front) view. The transverse processes of the vertebrae can be clearly seen.

THE OMOHYOID MUSCLE

The omohyoid muscle has two bellies connected by a tendon,the front portion lying just next to the sternohyoid muscle. It arises from the upper border of the scapula,passes through a tendinous loop attached to the clavicle, and then continues upward to insert on the hyoid bone.

THE MYLOHYOID MUSCLE

The mylohyoid muscle lies beneath the anterior belly of the digastric muscle and the stylohyoid muscle, and forms the whole floor of the mouth. It arises near the molars of the lower jaw and attaches all the way around the inner rim of the mandible. 

THE STYLOID MUSCLE

The styloid muscle is a slender muscle which arises from the styloid process of the temporal bone and passes straight down to insert on the body of the hyoid bone. If you look at the drawing of the skull’s side view, you can see the styloid process as a little finger of bone just below where the ear would be.

 THE DIGASTRIC MUSCLE

The digastric muscle becomes tendinous in the middle so that it can go through a fibrous ring which is attached to the hyoid bone. It arises in the rear of the mastoid process, a boney process just below and behind the ear, slopes down and forward though its ring on the hyoid bone and then swings forward to insert on the inside of the chin on the mandible.

 THE BONES OF THE NECK

 In this illustration you should note the first seven cervical vertebrae; three thoracic vertebrae; part of the shoulder girdle, made up of the scapula (partly seen), the clavicle and head of the humerus; the first two ribs; the clavicle, which goes from the spine of the scapula to the top of the sternum, the part called the manubrium; the hyoid bone; and a side view of the skull showing the occipital bone and the mastoid process. The hyoid bone is situated at the angle of the throat where the chin meets the neck just above the thyroid cartilage—the Adam’s Apple. It is the one bone in the body that is not articulated with another bone, rather it is held in place by the suprahyoid and infrahyoid muscles—those involved with swallowing.

Random fact: you can find your hyoid by putting your thumb and forefinger on either side of your trachea just below your jaw- you’ll know when you’ve found it because you can GENTLY push side to side with your fingers and you’ll feel it move. It’s rather bizarre feeling.

THE PTERYGOID MUSCLES

The pterygoid muscles, which are found on the inside of the ramus of the mandible, work together with the masseter muscle in chewing. There are of two of them, the lateral pterygoid muscle and the medial pterygoid muscle. The lateral muscle assists in opening the mouth, and they both assist in jaw rotation and side-to-side movement as well as in the projection of the lower jaw.The lateral pterygoid muscle is the more superior, or higher of the two muscles. 

THE MASSETER MUSCLE

 The jaw’s masseter muscle is one of the strongest muscles in the body. It is a very thick muscle, noticeable when someone clenches his teeth. It is the primary chewing muscle for closing the jaws. 

THE TEMPORALIS MUSCLE

The temporalis muscle helps to close the mouth, in grinding the teeth and to move the mouth from side to side when chewing. 

 THE ZYGOMATICUS MAJOR MUSCLE

The zygomaticus major muscle assists the risorious muscle in laughing and smiling by lifting the corners of the mouth.The modiolus is a tendinous tissue found at the corners of the mouth to which many of the muscles of expression attach.

 THE ZYGOMATICUS MINOR MUSCLE

The zygomaticus minor muscle is also a lip lifter and aids in smiling. 

THE LEVATOR LABII SUPERIORIS MUSCLE

The levator labii superioris muscle lies nasal to the zygomaticus minor muscle. It is the upper lip lifter, as its name implies. 

THE LEVATOR ANGULI ORIS MUSCLE

It translates from the Latin as “lifter of mouth at corners”

 THE LEVATOR LABII SUPERIORIS ALAEQUE NASI MUSCLE

The levator labii superioris alaeque nasi muscle is the most nasal of the levator labii muscles and is the one which allows you to sneer.

 THE DEPRESSOR ANGULI ORIS MUSCLE

The depressor anguli oris muscle of the lower lip aids in drawing the lower lip downward.

 THE DEPPRESSOR LABII INFERIORIS MUSCLE

The deppressor labii inferioris muscle is the main depressor or drawing down muscle of the lower lip. It lies next to the depressor anguli oris muscle, going toward the center, or medially.

 THE MENTALIS MUSCLE

The mentalis muscle allows you to dimple your chin when this muscles is contracted because it pulls on the skin. It is included with this group because in some people, but not all, fibers of this muscle arise from and mingle with the orbicularis oris. 

THE RISORIOUS MUSCLE

The risorious muscle is the “laughing muscle,” the one used when you laugh or smile.