The Supra- and Infrahyoid Muscles

Anatomy > Gray's Anatomy of the Human Body > IV. Myology > 5c. The Supra- and Infrahyoid Muscles

Henry Gray (1821–1865). Anatomy of the Human Body. 1918.

The Supra- and Infrahyoid Muscles

suprahyoid muscles

The suprahyoid muscles (Figs. 385, 386) are:

Digastricus.

Mylohyoideus.

Stylohyoideus.

Geniohyoideus.

Digastricus

The Digastricus (Digastric muscle) consists of two fleshy bellies united by an intermediate rounded tendon. It lies below the body of the mandible, and extends, in a curved form, from the mastoid process to the symphysis menti.

The posterior belly longer than the anterior, arises from the mastoid notch of the temporal bone and passes downward and forward. The anterior belly arises from a depression on the inner side of the lower border of the mandible, close to the symphysis, and passes downward and backward. The two bellies end in an intermediate tendon which perforates the Stylohyoideus muscle, and is held in connection with the side of the body and the greater cornu of the hyoid bone by a fibrous loop, which is sometimes lined by a mucous sheath. A broad aponeurotic layer is given off from the tendon of the Digastricus on either side, to be attached to the body and greater cornu of the hyoid bone; this is termed the suprahyoid aponeurosis

Variations are numerous. The posterior belly may arise partly or entirely from the styloid process, or be connected by a slip to the middle or inferior constrictor; the anterior belly may be double or extra slips from this belly may pass to the jaw or Mylohyoideus or decussate with a similar slip on opposite side; anterior belly may be absent and posterior belly inserted into the middle of the jaw or hyoid bone. The tendon may pass in front, more rarely behind the Stylohoideus.

Mentohyoideus muscle

The Mentohyoideus muscle passes from the body of hyoid bone to chin.

The Digastricus divides the anterior triangle of the neck into three smaller triangle

(1) the submaxillary triangle bounded above by the lower border of the body of the mandible, and a line drawn from its angle to the Sternocleidomastoideus, below by the posterior belly of the Digastricus and the Stylohyoideus, in front by the anterior belly of the Diagastricus;

(2) the carotid triangle bounded above by the posterior belly of the Digastricus and Stylohyoideus, behind by the Sternocleidomastoideus, below by the Omohyoideus;

(3) the suprahyoid or submental triangle bounded laterally by the anterior belly of the Digastricus, medially by the middle line of the neck from the hyoid bone to the symphysis menti, and inferiorly by the body of the hyoid bone.

http://www.wikimd.org/images/gray/large/image386.gif

FIG. 386– Muscles of the neck. Anterior view. (Picture From the Classic Gray's Anatomy)

Stylohyoideus

The Stylohyoideus (Stylohyoid muscle) is a slender muscle, lying in front of, and above the posterior belly of the Digastricus. It arises from the back and lateral surface of the styloid process, near the base; and, passing downward and forward, is inserted into the body of the hyoid bone, at its junction with the greater cornu, and just above the Omohyoideus It is perforated, near its insertion, by the tendon of the Digastricus.

Variations

It may be absent or doubled, lie beneath the carotid artery, or be inserted into the Omohyoideus, Thyreohyoideus, or Mylohyoideus.

The Stylohyoid Ligament (ligamentum stylohyoideus)

In connection with the Stylohyoideus muscle a ligamentous band, the stylohyoid ligament may be described. It is a fibrous cord, which is attached to the tip of the styloid process of the temporal and the lesser cornu of the hyoid bone. It frequently contains a little cartilage in its center, is often partially ossified, and in many animals forms a distinct bone, the epihyal

Mylohyoideus

The Mylohyoideus (Mylohyoid muscle), flat and triangular, is situated immediately above the anterior belly of the Digastricus, and forms, with its fellow of the opposite side, a muscular floor for the cavity of the mouth. It arises from the whole length of the mylohyoid line of the mandible, extending from the symphysis in front to the last molar tooth behind.

The posterior fibers pass medialward and slightly downward, to be inserted into the body of the hyoid bone. The middle and anterior fibers are inserted into a median fibrous raphé extending from the symphysis menti to the hyoid bone, where they joint at an angle with the fibers of the opposite muscle. This median raphé is sometimes wanting; the fibers of the two muscles are then continuous.

Variations

It may be united to or replaced by the anterior belly of the Digastricus; accessory slips to other hyoid muscles are frequent.

Geniohyoideus

The Geniohyoideus (Geniohyoid muscle) is a narrow muscle, situated above the medial border of the Mylohyoideus. It arises from the inferior mental spine on the back of the symphysis menti, and runs backward and slightly downward, to be inserted into the anterior surface of the body of the hyoid bone; it lies in contact with its fellow of the opposite side.

Variations

It may be blended with the one on opposite side or double; slips to greater cornu of hyoid bone and Genioglossus occur.

Nerves

The Mylohyoideus and anterior belly of the Digastricus are supplied by the mylohyoid branch of the inferior alveolar; the Stylohyoideus and posterior belly of the Digastricus, by the facial; the Geniohyoideus, by the hypoglossal.

Actions

These muscles perform two very important actions. During the act of deglutition they raise the hyoid bone, and with it the base of the tongue; when the hyoid bone is fixed by its depressors and those of the larynx, they depress the mandible. During the first act of deglutition, when the mass of food is being driven from the mouth into the pharynx, the hyoid bone and with it the tongue, is carried upward and forward by the anterior bellies of the Digastrici, the Mylohyoidei, and Geniohyoidei. In the second act, when the mass is passing through the pharynx, the direct elevation of the hyoid bone takes place by the combined action of all the muscles; and after the food has passed, the hyoid bone is carried upward and backward by the posterior bellies of the Digastrici and the Stylohyoidei, which assist in preventing the return of the food into the mouth.

Infrahyoid muscles

The infrahyoid muscles are:

Sternohyoideus.

Thyreohyoideus.

Sternothyreoideus.

Omohyoideus.

Sternohyoideus

The Sternohyoideus (Sternohyoid muscle) is a thin, narrow muscle, which arises from the posterior surface of the medial end of the clavicle, the posterior sternoclavicular ligament, and the upper and posterior part of the manubrium sterni. Passing upward and medialward, it is inserted by short, tendinous fibers, into the lower border of the body of the hyoid bone. Below, this muscle is separated from its fellow by a considerable interval; but the two muscles come into contact with one another in the middle of their course, and from this upward, lie side by side. It sometimes presents, immediately above its origin, a transverse tendinous inscription.

Variations

Doubling; accessory slips (Cleidohyoideus); absence.

Sternothyreoideus

The Sternothyreoideus (Sternothyroid muscle) is shorter and wider than the preceding muscle, beneath which it is situated. It arises from the posterior surface of the manubrium sterni, below the origin of the Sternohyoideus, and from the edge of the cartilage of the first rib, and sometimes that of the second rib, it is inserted into the oblique line on the lamina of the thyroid cartilage.

This muscle is in close contact with its fellow at the lower part of the neck, but diverges somewhat as it ascends; it is occasionally traversed by a transverse or oblique tendinous inscription.

Variations

Doubling; absence; accessory slips to Thyreohyoideus, Inferior constrictor, or carotid sheath.

Thyreohyoideus

The Thyreohyoideus (Thyrohyoid muscle) is a small, quadrilateral muscle appearing like an upward continuation of the Sternothyreoideus. It arises from the oblique line on the lamina of the thyroid cartilage, and is inserted into the lower border of the greater cornu of the hyoid bone.

Omohyoideus

The Omohyoideus (Omohyoid muscle) consists of two fleshy bellies united by a central tendon. It arises from the upper border of the scapula, and occasionally from the superior transverse ligament which crosses the scapular notch, its extent of attachment to the scapula varying from a few millimetres to 2.5 cm. From this origin, the inferior belly forms a flat, narrow fasciculus, which inclines forward and slightly upward across the lower part of the neck, being bound down to the clavicle by a fibrous expansion; it then passes behind the Sternocleidomastoideus, becomes tendinous and changes its direction, forming an obtuse angle.

It ends in the superior belly, which passes almost vertically upward, close to the lateral border of the Sternohyoideus, to be inserted into the lower border of the body of the hyoid bone, lateral to the insertion of the Sternohyoideus.

The central tendon of this muscle varies much in length and form, and is held in position by a process of the deep cervical fascia, which sheaths it, and is prolonged down to be attached to the clavicle and first rib; it is by this means that the angular form of the muscle is maintained.

Variations

Doubling; absence; origin from clavicle; absence or doubling of either belly.

The inferior belly of the Omohyoideus divides the posterior triangle of the neck into an upper or occipital triangle and a lower or subclavian triangle while its superior belly divides the anterior triangle into an upper or carotid triangle and a lower or muscular triangle

Nerves

The Infrahyoid muscles are supplied by branches from the first three cervical nerves. From the first two nerves the branch joins the hypoglossal trunk, runs with it some distance, and sends off a branch to the Thyreohyoideus; it then leaves the hypoglossal to form the descendens hypoglossi and unites with the communicantes cervicalis from the second and third cervical nerves to form the ansa hypoglossi from which nerves pass to the other Infrahyoid muscles.

Actions

These muscles depress the larynx and hyoid bone, after they have been drawn up with the pharynx in the act of deglutition. The Omohyoidei not only depress the hyoid bone, but carry it backward and to one or the other side. They are concerned especially in prolonged inspiratory efforts; for by rendering the lower part of the cervical fascia tense they lessen the inward suction of the soft parts, which would otherwise compress the great vessels and the apices of the lungs. The Thyreohyoideus may act as an elevator of the thyroid cartilage, when the hyoid bone ascends, drawing the thyroid cartilage up behind the hyoid bone. The Sternothyreoideus acts as a depressor of the thyroid cartilage.

Suprahyoid

Muscle	Origin	Insertion	Artery	Nerve	Action	Antagonist
digastric	Anterior belly: digastric fossa (mandible) Posterior belly: mastoid process of temporal bone	Intermediate tendon (lesser horn of hyoid bone)		Anterior belly: mandibular nerve [CNV3] via the mylohyoid nerve Posterior belly: facial nerve [CNVII]	Opens the jaw when the masseter and the temporalis are relaxed.
stylohyoid	styloid process (temporal)	greater cornu of hyoid bone		facial nerve [CNVII]	Elevate the hyoid during swallowing
mylohyoid	Mylohyoid line (mandible)	Median raphé	mylohyoid branch of inferior alveolar artery	mylohyoid nerve, from inferior alveolar branch of mandibular nerve [V3]	Raises oral cavity floor, elevates hyoid, depresses mandible
geniohyoid	Symphysis menti	Anterior surface of body of hyoid bone		C1 via hypoglossal nerve	Elevates the hyoid and the tongue upward during deglutition

Infrahyoid

Muscle	Origin	Insertion	Artery	Nerve	Action	Antagonistz
sternohyoid	manubrium of sternum	hyoid bone		Ansa cervicalis	depress hyoid bone
sternothyroid	manubrium	thyroid cartilage		Ansa cervicalis	Depresses larynx, may slightly depress hyoid bone.
thyrohyoid	thyroid cartilage	hyoid bone		C1	depress hyoid bone
omohyoid	Upper border of the scapula	Hyoid bone		Ansa cervicalis	Depresses the larynx and hyoid bone. Carries hyoid bone backward and to the side

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