The boundaries of the triangle are:
The anterior median plane of the neck medially; sternocleidomastoid laterally; base of the mandible and a line joining the angle of the mandible to the mastoid process, superiorly (Fig. 8.7).
Subdivisions
The anterior triangle encloses four suprahyoid and four infrahyoid muscles. The suprahyoid muscles
Hyoid bone Thyroid cartilage
Omohyoid (Superior belly)
Manubrium sterni
j. 8.5: The infrahyoid muscles.
Hyoid bone -Openings for internal laryngeal nerve and superior laryngeal vessels First tracheal ring Thyroid gland Fifth tracheal ring
Fig. 8.6: The thyroid gland, the larynx, and the trachea seen from the front.
Superior border of scapula -
Thyrohyoid W.— Oblique line
on thyroid cartilage
Stemothyroid — Sternohyoid
Omohyoid (Inferior belly)
- Clavicle I"~- First costal cartilage
,_ Thyrohyoid ligament —Thyrohyoid membrane —Oblique line on thyroid cartilage — Cricothyroid muscle - - Cricothyroid membrane Cricoid cartilage
Inferior belly of omohyoid
Fig. 8.7: The triangles of the neck. Note that the anterior and pos-
terior triangles are subdivided by the digastric and inferior belly of omohyoid muscles respectively.
are the digastric, the stylohyoid, the mylohyoid and the geniohyoid. The infrahyoid muscles, already examined, are the sternohyoid, the sternothyroid, the thyrohyoid and the omohyoid.
The anterior triangle is subdivided (by the digastric muscle and the superior belly of the omohyoid into: (a) Submental; (b) digastric; (c) carotid; and (d) muscular triangles (Fig. 8.7).
DISSECTION
Remove the deep fascia from anterior bellies of digastric muscles to expose parts of two mylohyoid muscles. Clean the boundaries and contents of the submental triangle.
Cut the deep fascia from the mandible and reflect it downwards to expose the submandibular gland. Identify and clean anterior and posterior bellies of digastric muscles, which form the boundaries of digastric triangle. Identify the intermediate tendon of digastric after pulling the submandibular gland laterally. Clean the stylohyoid muscle which envelops the tendon of digastric and is lying along with the posterior belly of digastric muscle. Identify the contents of digastric triangle.
Submental Triangle
This is a median triangle. It is bounded as follows. On each side there is the anterior belly of the corresponding digastric muscles. Its base is formed j by the body of the hyoid bone. Its apex lies at the chin. The floor of the triangle is formed by the right i and left mylohyoid muscles and the median raphe uniting them (Fig. 8.2).
Contents
1. Two to tour small submental lymph nodes are
situated in the superficial fascia between the anterior I bellies of the digastric muscles. They drain: (a) Superficial tissues below the chin; (b) central part of the lower lip; (c) the adjoining gum; (d) anterior part of the floor of the mouth; and (e) the tip of the tongue.
Their efferents pass to the submandibular nodes.
2. Small submental veins join to form the anterior
jugular veins.
Digastric Triangle
The area between the body of the mandible and the hyoid bone is known as the submandibular region. The superificial structures of this region lie in the submental and digastric triangles. The deep structures of the floor of mouth and root of the tongue will be studied separately at a later stage under the heading of Submandibular region (Chapter 11).
Boundaries: The boundaries of the digastric
triangle are as follows.
Anteroinferiorly: Anterior belly of digastric. Posteroinferiorly: Posterior belly of digastric and
the stylohyoid.
Superiorly or base: Base of the mandible and a
line joining the angle of the mandible to the mastoid process (Fig. 8.7).
Roof: The roof of the triangle is formed by :
1.Skin.
2.Superficial fascia, containing: (a) The plarysma;
(b) the cervical branch of the facial nerve; and (c) the ascending branch of the transverse or anterior cutaneous nerve of the neck.
3.Deep fascia, which splits to enclose the
submandibular salivary gland (Fig. 11.4).
Floor: The floor is formed by the mylohoid muscle
anteriorly, and by the hyoglossus posteriorly. A small part of the middle constrictor muscle of the pharynx, appears in the floor (Figs 8.8, 8.9).
Suprac/awcu/ar part Occipital part Digastric triangle Chin Half sub-mental triangle Carotid triangle Muscular triangle Superior belly of omohyoid
i
Anterior triangle parts: Posterior triangleContents
Anterior Part of the Triangle
1.Structures superficial to mylohyoid are: (a)
Superficial part of the submandibular salivary gland (Fig. 8.2). The facial vein and the submandibular lymph nodes are superficial to it and the facial artery is deep to it; (b) submental artery; (c) mylohyoid nerve and vessels.
2.Structures superficial to the hyoglossus seen
without disturbing the mylohyoid and the submandibular gland are: (a) The submandibular salivary gland: (b) the intermediate tendon of the digastric and the stylohyoid; and (c) the hypoglossal nerve
(Fig. 11.2). Other relations will be studied in the submandibular region.
Posterior Part of the Triangle
1.Superficial structures are: (a) Lower part of the
parotid gland, and (b) the external carotid artery before it enters the parotid gland.
2.Deep structures, passing between the external
and internal carotid arteries are: (a) The
styloglossus; (b) the stylopharyngeus; (c) the glossopharyngeal nerve; (d) the pharyngeal branch of the vagus nerve; (e) the styloid process; and (f) a part of the parotid gland (Fig. 9.4).
Stylogossus - Sublingual gland Mylohyoid line Lingual nerve_______[ Stylohyoid ligament -____* Submandibular duct--- Middle constrictor of pharynx ——_f, 1'
- " \ k 3 t /X^ ' Superficial part submandibular gland
Lingual artery " >35j£-x' \
Greater cornua of hyoid bone - - / \ Hypogtossal nerve
Investing fascia " "; Common tendon of digastric muscle Fig. 8.8:
Coronal section through the digastric triangle and the submandibular region.
Posterior belly of digastric Middle and
inferior constrictors of pharynx
Facial artery Hyoglossus Anterior belly of digastric
Mylohyoid Masseter
Mylohyoid muscle
Deep part of submandibular gland Hyoglossus muscle
Hyoid with pulley for tendon of digastric bellies
126 Head and Neck
3. Deepest structures include: (a) The internal carotid artery, (b) the internal jugular vein, and (c) the vagus nerve.
The deep structures will be studied with the submandibular region.
The submandibular lymph nodes are clinically very important because of their wide area of drainage. They are very commonly enlarged. The nodes lie beneath the deep cervical fascia on the surface of the submandibular salivary gland. They drain:
(a) The centre of the forehead; (b) the nose with the
frontal, maxillary and ethmoidal air sinuses; (c) the inner canthus of the eye; (dj the upper lip and the anterior part of the cheek with the underlying gum and teeth; (e) the outer part of the lower lip with the lower gum and teeth excluding the incisors; (fj the anterior two-thirds of the tongue excluding the tip, and the floor of the mouth. They also receive efferents from the submental lymph, nodes. The
efferents from the submandibular nodes pass mostly
to the jugulo-omohyoid node and partly to the jugulo- digastric node. These nodes are situated along the internal jugular vein and are members of the deep cervical chain (Figs 2.25, 12.29).
Carotid Triangle
Boundaries
Anterosuperiorly: Posterior belly of the digastric
muscle; and the stylohyoid (Fig. 8.7).
Anteroinferiorly: Superior belly of the omohyoid. Posteriorly: Anterior border of the sternocleido-
mastoid muscle.
DISSECTION
Clean the area situated between posterior belly of digastric and superior belly of omohyoid muscle, to expose the three carotid arteries with internal jugular vein. Trace IX, X, XI and XII nerves in relation to these vessels.
Carefully clean and preserve superior root, the loop and inferior root of ansa cervicalis in relation to anterior aspect of carotid sheath. Locate the sympathetic trunk situated posteromedial to the carotid sheath. Dissect the branches of external carotid artery.
Identify and preserve internal laryngeal nerve in the thyrohyoid interval. Trace it postero- superiorly till vagus. Also look for external laryngeal nerve supplying the cricothyroid muscle.
The carotid triangle provides a good view of all the large vessels and nerves of the neck, particularly when its posterior boundary is retracted slightly backwards.
Roof
1.Skin.
2.Superficial fascia containing: (a) The plastysma; (b) the cervical branch of the facial nerve; and (c) the transverse cutaneous nerve of the neck. 3.Investing layer of deep cervical fascia.
Floor
It is formed by parts of (a) The thyrohyoid muscle; (b) the hyoglossus; (c) and the middle and inferior constrictors of the pharynx (Fig. 8.10).
Contents
Arteries: (1) The common carotid artery with the. i
carotid sinus and the carotid body at its termination; j (2) internal carotid artery; and (3) the external carotid artery with its superior thyroid, lingual, facial, ascending pharyngeal and occipital, branches (Fig. 8.11).
Veins: (1) The internaljugularvein; (2) the common facial vein draining into the internal jugular vein; (3) a pharyngeal vein which may end either in the internal jugular vein or in the common facial vein; and (4) the lingual vein which usually terminates in the internal jugular vein, but may drain into the common facial vein.
Nerves: (1) The vagus running vertically
downwards; (2) the superior laryngeal branch of the vagus, dividing into the external and internal laryngeal nerves; (3) the spinal accessory nerve running backwards over the internal jugular vein; and the (4) the hypoglossal nerve running forwards over the external and internal carotid arteries. The hypoglossal nerve gives off the upper root of the ansa cervicalis or descendens hypoglossi, and another branch to the thyrohyoid. (5) The sympathetic chain runs (Fig. 8.12) vertically downwards posterior to the carotid sheath (Fig. 12.4).
Carotid sheath with its contents.
Lymph nodes: The deep cervical lymph nodes are
situated along the internal jugular vein, and include the jugulodigastric node below the posterior belly of the digastric and the jugulo-omohyoid node above the inferior belly of the omohyoid (Fig. 12.29).
Common Carotid Artery
The right common carotid artery is a branch of the brachiocephalic artery. It begins in the neck behind the right sternoclavicular joint. The left common carotid artery is branch of the arch of the aorta. It begins in the thorax in front of the trachea opposite a point a little to the left of the centre of the
Stylohyoid ligament Hyoglossus Mylohyoid
Anterior Triangle of the Neck 127 - ~ Styloid process
-— Upper border of triangle formed by posterior belly of digastric
--- Middle constrictor
i
• M/IUIU i.uiv>ieiy<?---- -f-.
Thyrohyoid muscle---V— ';<> Insertion of sternohyoid (on oblique line)
Cricothyroid membrane--- Cricoid cartilage —-
Trachea---
_____Thyrohyoid membrane (with openings for internal laryngeal nerve and superior laryngeal vessles
"—- Inferior constrictor
"~^^. Lateral border of triangle formed by anterior border of sternocleidomastoid
~* Medial border of triangle formed by superior belly of omohyoid
~ Oesophagus "~ Recurrent laryngeal nerve
Fig. 8.10: Floor of the carotid triangle.
fig. 8.11: Carotid arteries, branches of the external carotid artery, and the internal jugular vein, in relation to the carotid triangle,
manubrium. It ascends to the back of the left sternoclavicular joint and enters the neck (Fig. 12.11). In the neck, both arteries have a similar course. Each artery runs upwards within the carotid sheath, under cover of the anterior border of the sternocleidomastoid. It lies in front of the lower four cervical transverse processes. At the level of the upper border of the thyroid cartilage the artery ends
by dividing into the external and internal carotid
arteries (Fig. 8.12).
Carotid Sinus
The termination of the common carotid artery, or the beginning of the internal carotid artery shows a slight dilatation, known as the carotid sinus. In this region, the tunica media is thin, but the adventitia is relatively thick and receives a rich innervation from the glossopharyngeal and sympathetic nerves. The carotid sinus acts as a baroreceptor or pressure
receptor and regulates blood pressure.
Carotid Body
Carotid body is a small, oval reddish-brown structure situated behind the bifurcation of the common carotid artery. It receives a rich nerve supply mainly from the
Superficial temporal
artery Maxillary artery - Internal carotid
Posterior auricular ,*'' artery
External carotid artery
Facial artery — Occipital artery — Internal jugular vein ~ Ascending pharyngeal ^f — Carotid sinus
Outline of carotid triangle
Lingual artery — Superior thyroid artery -
Carotid body Common carotid artery
glossopharyngeal nerve, but also from the vagus and sympathetic nerves. It acts as a chemoreceptor and responds to changes in the oxygen and carbon dioxide and pH content of the blood.
Other allied chemoreceptors are found near the arch of the aorta, the ductus arteriosus, and the right subclavian artery. These are supplied by the vagus nerve.
External Carotid Artery
External carotid artery is one of the terminal branches of the common carotid artery. In general, it lies anterior to the internal carotid artery, and is the chief artery of supply to structures in the front of the neck and in the face (Figs 8.11, 8.12).
External laryngeal nerve -
Superior thyroid artery — Superior root of ansa cervicalis
Fig. 8. 12: The ninth, tenth, eleventh and twelfth cranial nerves and their branches related to the carotid arteries and to the internal jugular vein, in and around the carotid triangle.
Surface Marking
The external carotid artery is marked by joining the following two points.
(a)A point on the anterior border of the sterno- cleidomastoid muscle at the level of the upper border of the thyroid cartilage.
(b)A second point on the posterior border of the neck of the mandible.
The artery is slightly convex forwards in its lower half and slightly concave forwards in its upper half (Fig. 12.10).
Course and Relations
1.The external carotid artery begins in the carotid triangle at the level of the upper border of the thyroid cartilage opposite the disc between the third and fourth cervical vertebrae. It runs
upwards and slightly backwards and laterally, and terminates behind the neck of the mandible by dividing into the maxillary and superficial temporal arteries.
2.The external carotid artery has a slightly curved
course, so that it is anteromedial to the
internal carotid artery in its lower part, and anterolateral to the internal carotid artery in its upper part.
3.In the carotid triangle, the external carotid artery
is comparatively superficial, and lies under cover of the anterior border of the sternocleidomastoid. The artery is crossed superficially by the cervical branch of the facial nerve, the hypoglossal nerve, and the facial, lingual and superior thyroid veins. Deep to the artery there are: (1) The wall of the pharynx; (2) the superior laryngeal nerve which divides into the
external and internal laryngeal nerves; and (3) the ascending pharyngeal artery (Fig. 8.10).
4. Above the carotid triangle the external carotid artery lies deep in the substance of the parotid gland. Within the gland, it is related superficially to the retromandibular vein and the facial nerve (Fig. 9.4). Deep to the external carotid artery, there are: (a) The internal carotid artery; (b) structures passing between the external and internal carotid arteries; these being styloglossus, stylopharyngeus, IXth nerve, pharyngeal branch of Xth, and styloid process; and (c) two structures deep to the internal carotid artery, namely the superior laryngeal nerve and the superior cervical sympathetic ganglion (Fig. 8.12).
Branches
The external carotid artery gives off eight branches which may be grouped as follows.
Anterior: (1) Superior thyroid; (2) lingual; and (3)
facial.
Posterior: (1) Occipital; and (2) posterior auricular. Medial: Ascending pharyngeal.
Terminal: (I) Maxillary; and (2) superficial temporal
(Fig. 8.12).
Superior Thyroid Artery
The superior thyroid artery arises from the external carotid artery just below the level of the greater cornua of the hyoid bone. It runs downwards and forwards parallel and just superficial to the external laryngeal nerve. It passes deep to the three long infrahyoid muscles to reach the upper pole of the
External carotid artery Styloid process Internal carotid artery Glossopharyngeal nerve •._ Pharyngeal branch of vagus---
Accessory nerve
^---- Occipital artery
~"~ Outline of carotid triangle ""• Superior laryngeal branch of vagus --- Vagus nerve
--- Inferior root of ansa cervicalis Hypoglossal nerve _^
Internal laryngeal nerve---
lateral lobe of the thyroid gland. Its relationship to the external laryngeal nerve, which supplies the cricothyroid muscle is important to the surgeon during thyroid surgery) The artery and nerve are close to each other higher up, but diverge slightly near the gland. To avoid injury to the nerve, the superior thyroid artery is ligated as near to the gland as possible (Fig. 12.6).
Apart from its terminal branches to the thyroid gland, it gives one important branch, the superior
laryngeal artery which pierces the thyrohyoid
membrane in company with the internal laryngeal nerve (Fig. 8.6). The superior thyroid artery also gives a sternocleidomastoid branch to that muscle and a cricothyroid branch that anastomoses with the artery of the opposite side in front of the cricovocal membrane (Fig. 12.6).
Lingual Artery
The lingual artery arises from the external carotid artery opposite the tip of the greater cornu of the hyoid bone (Fig. 8.12).
Its course is divided into three parts by the hyoglossus muscle. The first part lies in the carotid triangle. It forms a characteristic upward loop which is crossed by the hypoglossal nerve (Fig. 11.2). The lingual loop permits free movements of the hyoid bone. The second part lies deep to the hyoglossus along the upper border of hyoid bone. It is superficial to the middle constrictor of the pharynx. The third
part is called the arteria profunda linguae, or the
deep lingual artery. It runs upwards along the anterior border of the hyoglossus, and then horizontally forwards on the undersurface of the tongue as the
fourth part. In its vertical course, it lies between the
genioglossus medially and the inferior longitudinal muscle of the tongue laterally. The horizontal part of the artery is accompanied by the lingual nerve.
During surgical removal of the tongue, the first part of the artery is ligated before it gives any branch to the tongue or to the tonsil.
Facial Artery
The facial artery arises from the external carotid just above the tip of the greater cornua of the hyoid bone. It runs upwards first in the neck as cervical part and then on the face as facial part. The course of the artery in both places is tortuous. The tortuosity in the neck allows free movements of the pharynx during deglutition. On the face it allows free movements of the mandible, the lips and the cheek during mastication and during various facial expressions. The artery escapes traction and pressure during these movements.
The cervical part of the facial artery runs upwards on the superior constrictor of pharynx deep to the posterior belly of the digastric, with the stylohyoid and to the ramus of the mandible. It grooves the posterior border of the submandibular salivary gland. Next the artery makes an S-bend (two loops) first winding down over the submandibular gland, and then up over the base of the mandible (Figs 11.7, 11.8). The course and branches of the facial part of the facial artery have been described with the face (Fig. 2.21).
The cervical part of the facial artery gives off the ascending palatine, tonsillar, submental, and glandular branches for the submandibular salivary gland and lymph nodes. The ascending palatine
artery arises near the origin of the facial artery. It
passes upwards between the styloglossus and the stylopharyngeus, crosses over the upper border of the superior constrictor and supplies the tonsil and the root of the tongue. The submental branch is a large artery which accompanies the mylohyoid nerve, and supplies the submental triangle and the sublingual salivary gland.
Occipital Artery
The occipital artery arises from the posterior aspect of the external carotid artery, opposite the' origin of the facial artery. It is crossed at its origin by the hypoglossal nerve. In the carotid triangle, the artery gives two sternocleidomastoid branches. The upper branch accompanies the accessory nerve, and the lower branch arises near the origin of the occipital artery. The further course of the artery has been described in Chapter 4 (Figs 8.11, 4.2, 4.5).