Download Unit 14: Anterior Triangle of the Neck Submandibular region

Unit 14:
Anterior Triangle of the Neck
Submandibular region
Dissection Instructions:
Review the landmarks and cutaneous innervation (Plates 20, 25, 27, 28; 8.3) of the neck. Review
the strap (infrahyoid) muscles and their nerve supply, the ansa cervicalis (Plates 23-25, 27; 8.10,
8.16A-C, Table 8.5 and figures-p. 740). Review the fascias of the neck (Plate 31; 8.1).
Find and review the relationship of the phrenic nerve to the scalenus anterior muscle, the
ascending cervical artery paralleling the phrenic nerve, the vertebral artery, other branches of the first
part of the subclavian artery and the junction of the subclavian vein with the internal jugular vein
(Plates 28, 29; 8.3, 8.20, 8.22 ).
Clean the submandibular gland (Plates 56, 57, 65, 69; 8.8), keeping its blood supply intact. Its
nerve supply from the lingual nerve and submandibular ganglion enter the gland on its upper border.
The lingual nerve comes from deep in the infratemporal fossa and enters the tongue by passing between
the hyoglossus and mylohyoid muscles. The preganglionic fibers arriving at the submandibular
ganglion belong to the facial nerve and they join the lingual nerve high in the infratemporal fossa. The
deep part of the gland contains the duct which enters the mouth by passing deep to the mylohyoid muscle.
The blood supply is from the facial artery which usually goes deep to the gland before crossing
superficial to the lower margin of the mandible to enter the face.
Clean the digastric and stylohyoid muscles (Plates 49, 55, 57; 8.9-8.11). The digastric muscle
has anterior and posterior bellies with an intermediate tendon held to the hyoid bone by means of a
connective tissue pulley. The posterior belly arises from the medial side of the mastoid process. The
posterior belly is soon joined by the stylohyoid muscle arising from the adjacent styloid process. Near the
hyoid bone, the stylohyoid muscle usually splits, encircling the intermediate tendon of the digastric,
before inserting on the hyoid bone. The anterior belly of the digastric inserts on the deep side of the
mandibular symphysis. The digastric muscle and the lower border of the mandible form the boundaries
of the digastric or submandibular triangle. Within the triangle locate the nerve to the mylohyoid muscle
in company with the submental vessels (Plates 42; 8.11). The nerve to the mylohyoid muscle is a branch
of the inferior alveolar branch of the mandibular division of the trigeminal nerve. It also supplies
the anterior belly of the digastric muscle. The posterior belly of the digastric muscle and the stylohyoid
muscle are supplied by the facial nerve, but this can not be seen at this time.
Deep to the anterior belly of the digastric muscle is the mylohyoid muscle (Plates 49; 8.11, 8.12,
8.15). Its fibers arise on the mylohyoid line on the inner surface of the body of the mandible. It inserts on
a mid-line raphe and on the upper surface of the hyoid bone. Clean the posterior border of the mylohyoid
muscle and locate the hypoglossal nerve, duct of the submandibular gland and the lingual nerve. All
three structures enter the mouth by passing deep to the mylohyoid muscle and superficial to the
hyoglossus muscle (Plates 55, 57, 67; 8.11, 8.12). This latter muscle runs vertically from its origin on
the hyoid bone to the side of the tongue. Passing deep to the hyoglossus muscle are the lingual artery
(Plates 55, 65, 67; 8.13A&B, 8.14) and glossopharyngeal nerve. The nerve should not be seen at this
time.
Clean the common carotid artery in the neck (Plates 28, 29, 65, 67; 8.9, 8.10). On the right
side the common carotid arises from the brachiocephalic artery and on the left from the aortic arch,
Unit 14 - 1
but in the neck, they are symmetrically placed at the sides of the trachea and larynx. Near the upper
border of the thyroid cartilage of the larynx the common carotid dilates, divides and forms the external
and internal carotid arteries. The dilatation is the carotid sinus, which is active in blood pressure
control through its pressure receptors. The nerve which carries sensory information from the carotid sinus
lies between the external and internal carotids and branches from the glossopharyngeal nerve. It is aptly
named the nerve to the carotid sinus. The external carotid artery is anterior to the internal carotid
artery.
Locate and clean the branches of the external carotid artery (Plates 65; 8.6). Three branches
arise from the anterior aspect of the external carotid artery in this area of dissection, the superior thyroid,
lingual and facial arteries. The lowest branch is the superior thyroid artery. On its way to the thyroid
gland, it gives off the superior laryngeal artery which pierces the thyrohyoid membrane to enter the
larynx. Immediately above the superior laryngeal vessels is the internal branch of the superior
laryngeal nerve. Near the level of the hyoid bone is the origin of the lingual artery. It goes deep to the
hyoglossus muscle within 5 mm of the hyoid bone. The facial artery arises above the origin of the
lingual artery, sometimes with it, and disappears under the submandibular gland.
The ascending pharyngeal artery arises from the medial or posterior surface of the external
carotid artery. It ascends vertically on the lateral wall of the pharynx. The posterior surface of the
external carotid gives off the occipital artery. This vessel ascends and moves posteriorly to go deep to
the mastoid process. It was seen in Unit 1 in company with the greater occipital nerve. The
hypoglossal nerve descends from behind both carotid arteries and hooks under the occipital artery before
crossing superficial to both carotids, then passes between the mylohyoid and hyoglossus muscles to
supply the tongue (Plates 28, 30, 55, 65, 67; 8.9-8.13). The hypoglossal nerve is the motor nerve to the
tongue, innervating all its muscles. Paralysis of one hypoglossal nerve causes the protruded tongue to
point to the side of the lesion.
Clean the internal jugular vein (Plates 27, 66, 70; 8.4, 8.5, 8.8) without destroying its
tributaries. It lies lateral to the carotid arteries and deep to the sternocleidomastoid muscle. High in the
neck, the internal jugular vein receives the common facial vein anteriorly and the occipital vein
posteriorly. The common facial vein is formed by the facial vein and the anterior branch of the
retromandibular vein. The superior thyroid vein empties into the internal jugular vein below the
common facial vein. At the level of the thyroid gland, the middle thyroid vein flows into the internal
jugular. The transverse cervical and suprascapular veins empty into the external jugular vein fairly
low in the neck. The external jugular vein empties into the subclavian vein low in the neck. It is
formed from the posterior auricular vein and the posterior branch of the retromandibular vein.
Clean the vagus nerve. It travels between and posterior to the carotid arteries and the internal
jugular vein (Plates 67, 71; 8.20, 8.21). High in the neck, above the level of this dissection, the vagus
gives off the superior laryngeal nerve. The pharyngeal branches of the vagus pass between the
carotid arteries to reach the pharyngeal wall. In the neck, the vagus also gives off the superior and
inferior cervical cardiac nerves. These carry parasympathetic fibers to the heart.
Locate again the internal branch of the superior laryngeal nerve entering the larynx and clean
it upwards towards its origin from the vagus nerve. It travels deep to both carotid arteries, where it
separates from the external branch (Plates 67, 70, 71, 76; 8.21, 8.28 and figures- p. 766). The external
branch of the superior laryngeal nerve supplies the small cricothyroid muscle and part of the inferior
pharyngeal constrictor (Plates 67, 72; 8.10).
Unit 14 - 2
Locate the sympathetic trunk lying on the vertebral column behind the carotid sheath structures
(Plates 124; 8.20, 8.21, 8.24, figure-p. 760). In cleaning it, keep in mind that it has numerous small
branches. Follow the trunk upwards until it enlarges into the large superior cervical ganglion. This
ganglion supplies four gray communicating rami to the first four cervical nerves, probably indicating that
it is the result of fusion of four ganglia. It also communicates with cranial nerves IX, X and XII and gives
off the superior cervical sympathetic cardiac nerve. The middle cervical ganglion is very small and is
located at about the level of the CV6. It has two gray communicating rami and the middle cervical
sympathetic cardiac nerve. The inferior cervical ganglion has two gray communicating rami and the
inferior cervical sympathetic cardiac nerve. The inferior cervical ganglion may be fused to the first
thoracic ganglion forming the stellate ganglion, and there may be a vertebral ganglion near the
vertebral artery.
Be sure to identify all of the following in this unit:
submandibular gland
digastric muscle (ant & post bellies)
stylohyoid muscle
nerve to mylohyoid muscle
submental vessels
mylohyoid muscle
hypoglossal nerve
duct of submandibular gland
lingual nerve
hyoglossus muscle
carotid sheath
common carotid artery
internal carotid artery
external carotid artery
carotid sinus
superior thyroid artery
superior laryngeal artery
lingual artery
facial artery
ascending pharyngeal artery
occipital artery
internal branch of superior laryngeal nerve
external branch of the superior laryngeal nerve
internal jugular vein
facial vein
occipital vein
retromandibular vein
posterior auricular vein
external jugular vein
vagus nerve
pharyngeal branches of the vagus nerve
superior & inferior cardiac nerves (vagal)
sympathetic trunk
superior cervical ganglion
gray communicating rami to cervical nerves
middle and inferior cervical/stellate ganglia
superior & inferior cardiac nerves (sympathetic)
Unit 14 - 3