This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The carotid arteries and their branches are found in this triangle. The line of the carotid arteries is from a mid-point between the mastoid process and the angle of the jaw to the sternoclavicular articulation. The line of the sternomastoid muscle is from the mastoid process to near the middle of the upper edge of the sternum. Thus the carotids are internal to the anterior edge of this muscle above, behind the angle of the jaw, and external to it below. The common carotid at its upper portion - it ends opposite the upper border of the thyroid cartilage - is just about at or close to the edge of the sternomastoid muscle. From the thyroid cartilage up are the internal and external carotids. The internal lies behind and to the outer side of the external. The internal gives off no branches until it reaches the skull, while the external is practically all branches. Sometimes the external and the internal carotids are covered by the anterior margin of the sternomastoid muscle. The branches of the external carotid are the superior thyroid, ascending pharyngeal, lingual, facial, occipital, posterior auricular, internal maxillary, and temporal. The superior thyroid or the ascending pharyngeal may either one be the first given off by the external carotid, or may come off from the common carotid itself just before its bifurcation.
The superior thyroid artery is given off in the interval between the hyoid bone and upper border of the thyroid cartilage. It gives a small infrahyoid branch to the thyrohyoid membrane, also a superior laryngeal branch to the inside of the larynx. This branch pierces the thyrohyoid membrane in company with the superior laryngeal nerve to reach the interior of the larynx. The sternomastoid branch, to the muscle of that name, comes off at this point and crosses the common carotid artery. It is of some importance on this account because in ligating the common carotid artery above the omohyoid muscle it is likely to be cut and cause bleeding. Another branch of the superior thyroid artery is the cricothyroid. It is small, rests on the cricothyroid membrane, and is the first artery liable to be cut in an incision down the median line. Bleeding from it is not apt to be serious. 1 he remainder of the superior thyroid artery supplies the thyroid gland.
Fig. 166. - Submaxillary region - mylohyoid muscle cut away showing the sublingual gland and anterior portion of submaxillary gland.
The ascending pharyngeal is a long slender branch that comes from the under side of the main trunk. It lies on the superior and middle constrictors of the pharynx and goes clear to the skull, giving off some meningeal branches. In ligating the external carotid care should be taken not to include this vessel in the ligature. It also gives branches to the soft palate, tonsil, recti capitis antici muscles, and tympanum.
The lingual is given off just below the greater horn of the hyoid bone, and passes forward beneath the hyoglossus muscle to supply the tongue and sublingual tissues. The hypoglossal nerve lies above the artery and on the hyoglossus muscle.
The facial comes off just above the lingual artery or often in a common trunk with it. It passes upward and forward in a groove in the under surface of the submaxillary gland and passes over the edge of the jaw at the anterior border of the masseter muscle. The facial vein at this point is posterior to it.
The occipital artery comes off almost opposite the facial. It passes upward and backward between the mastoid process and the transverse process of the atlas, then along in the occipital groove beneath the origin of the sternomastoid muscle, the splenius, trachelomastoid, and digastric to make its appearance a little to the inner side of the middle of a line joining the mastoid process with the external occipital protuberance.
The posterior auricular is given off just above the posterior belly of the digastric muscle and runs backward and upward on it, then through the parotid gland and up between the external auditory meatus and the mastoid process. In ligating the external carotid artery with a view of preventing bleeding in removing the Gasserian ganglion, it is endeavored to place the ligature just above the digastric muscle and posterior auricular artery in order to preserve the blood supply of the tissues above and behind the ear. The internal maxillary and the temporal arteries have already been considered.
Fig. 167. - Carotid arteries and branches.