The carotid triangle is bound by the sternocleido- mastoid behind, the posterior belly of the digas- tric superiorly, and the superior belly of the omo- hyoid inferiorly [Fig. 6.2]. It contains the vertical
Fig. 6.5 Lateral view of the constrictors of the pharynx and associated muscles.
Levator palati M.
Tensor palati M.
Styloid process Styloglossus M.
Stylohyoid M.
Superior constrictor M.
Superior laryngeal N. and A.
External laryngeal N.
Recurrent laryngeal N.
Trachea Cricothyroid M.
Thyroid cartilage Thyrohyoid M.
Hyoglossus M.
Hyoid bone Mylohyoid M.
Parotid duct Buccinator M.
Inferior laryngeal A.
Oesophagus Cricoid cartilage Stylopharyngeus M.
Pterygomandibular raphe
Styloglossus M.
Stylohyoid M.
Middle constrictor M.
Inferior constrictor M.
Stylopharyngeus M.
Glossopharyngeal N.
58
The anterior triangle of the neck
the external carotid artery, and finer details of its branches, are described with the deeper dissection of the neck—Chapter 9.)
1. The superior thyroid artery curves antero- inferiorly and disappears deep to the omohyoid. It gives off the infrahyoid, sternocleidomastoid, and superior laryngeal branches in the triangle. The su- perior laryngeal artery enters the larynx with the internal laryngeal nerve.
2. The ascending pharyngeal artery arises from the lowest part of the external carotid artery. It jugular vein descends vertically, first with the in-
ternal and then the common carotid artery medial to it.
External carotid artery
The external carotid artery begins at the upper border of the thyroid cartilage as a branch of the common carotid artery. It ascends along the side of the pharynx, anteromedial to the internal ca- rotid artery. It gives off the following branches in the carotid triangle [Fig. 6.7]. (The full extent of
DISSECTION 6.5 Carotid triangle Objective
I. To study the boundaries and contents of the carotid triangle [Fig. 6.4].
Instructions
1. Remove the fat and fascia from the area between the posterior belly of the digastric and the supe- rior belly of the omohyoid [Fig. 6.2].
2. Expose the internal jugular vein laterally, the com- mon and internal carotid arteries medial to it, and the external carotid artery anteromedial to the in- ternal carotid artery.
3. Find the facial and lingual veins entering the internal jugular vein in the upper part of the triangle, and the superior thyroid vein entering it in the lower part.
4. Between the vein and the internal carotid artery, find the hypoglossal nerve. Follow it forwards across the external carotid artery, and find the fol- lowing branches in the carotid triangle: (1) the su- perior root of the ansa cervicalis, given off where the nerve hooks round the occipital artery to enter the triangle; and (2) the branch to the thyrohyoid muscle given off as the hypoglossal leaves the ca- rotid triangle [Fig. 6.4].
5. Remove the superficial part of the carotid sheath which surrounds the internal jugular vein, carotid arteries, and vagus nerve. Avoid injury to the superior root of the ansa cervicalis anterior to the vein and to its inferior root lateral to the vein. (The inferior root of the ansa cervicalis arises from the second and third cervical ventral rami. The two roots unite to form a loop—the ansa cervicalis—at a lower level.)
6. Expose the external carotid artery and its branch- es [Figs. 6.6, 6.7]. The superior thyroid is the lowest
branch in the carotid triangle [Fig. 6.7]. The lingual, facial, and occipital arteries arise in the upper part of the triangle; the occipital artery arises opposite the facial artery [Fig. 6.7].
7. Find the internal laryngeal nerve in the interval be- tween the hyoid bone and thyroid cartilage [Fig. 6.6].
Trace it posterosuperiorly, deep to the carotid arter- ies, to the parent stem, the superior laryngeal branch of the vagus. From the superior laryngeal nerve, fol- low the slender external laryngeal nerve downwards, deep to the superior thyroid artery [Fig. 6.5].
8. Expose the part of the hyoglossus which lies in the carotid triangle immediately above the hyoid bone. Note the hypoglossal nerve on its surface, and the lingual artery lying deep to it. The lingual artery lies on the middle constrictor of the phar- ynx [Fig. 6.5], which separates it from the mucous membrane of the pharynx.
9. Raise the posterior belly of the digastric to expose the middle constrictor at the hyoid bone [Fig. 6.5].
10. Find the thyrohyoid muscle in the floor of the car- otid triangle.
11. Push the superior thyroid and carotid arteries pos- teriorly, and remove the fat surrounding the exter- nal laryngeal nerve. This exposes a part of the in- ferior constrictor muscle which passes backwards from the side of the thyroid cartilage.
12. Separate the internal and common carotid arter- ies from the internal jugular vein, and expose the vagus nerve in the posterior part of the carotid sheath between them. Pull the arteries antero- medially, and find the sympathetic trunk postero- medial to the sheath.
59
Subdivisions of the anterior triangle
Fig. 6.6 Deep dissection of the submandibular region.
Masseter M.
Inferior alveolar N. and A.
Styloglossus M.
Stylopharyngeus M. and glossopharyngeal N.
Parotid gland
Lingual A.
Hypoglossal N.
Sternocleidomastoid
Thyrohyoid M.
Superior laryngeal A.
and internal laryngeal N.
Hyoglossus M.
Submental A.
Mylohyoid N.
Mylohyoid M.
Last molar tooth
Submandibular gland, deep part Inferior alveolar A. and N.
Lingual N.
Medial pterygoid M.
Fig. 6.7 External carotid artery and its branches. The mandible has been tilted upwards.
Superficial temporal A.
Maxillary A.
Posterior auricular A.
External carotid A.
Internal carotid A.
Occipital A.
Sternocleidomastoid A.
Sternocleidomastoid A.
Omohyoid
Common carotid A.
Hypoglossal N.
Ascending pharyngeal A.
Superior root, ansa cervicalis Superior thyroid A.
Sternohyoid Superior laryngeal A.
Laryngeal prominence Infrahyoid A.
Hyoid bone Facial A.
Submental A.
Lingual A.
60
The anterior triangle of the neck
inferior root of the ansa cervicalis arises from the ventral rami of the second and third cervical nerves behind the internal jugular vein. It curves for- wards, usually on the lateral surface of the vein, and passes down on the common carotid artery. Here it joins the superior root from the hypoglossal nerve.
The loop lies at the level of the lower part of the lar- ynx.
The ansa cervicalis consists of nerve fibres from the cervical ventral rami of C. 1, C. 2, and C. 3. It supplies the infrahyoid muscles—sternohyoid, sternothyroid, and omohyoid. The thyrohyoid and geniohyoid are supplied by C. 1 fibres which run along with the hypoglossal nerve [see Fig. 16.3]. (In this way, the hypoglossal nerve forms a secondary plexus with the first three cervical ventral rami.) Together they supply a ventral strip of muscle from the tongue to the sternum.