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.
Of recent years the external carotid artery has been ligated far more often than formerly, as it was customary to ligate the common carotid instead. The external carotid runs from the upper border of the thyroid cartilage to the neck of the mandible. It supplies the outside of the head, face, and neck. These parts are the seat of various operations for tumors, especially carcinoma of the mouth and tongue, diseased lymph-nodes, and other affections, and the external carotid and its branches are not infrequently ligated in order to cut off their blood supply.
Fig. 173. - Ligation of external carotid artery and its branches.
In extirpation of the Gasserian ganglion, hemorrhage has been such an annoying and dangerous factor that a preliminary ligation or compression (Crile) of the external carotid is frequently resorted to. This artery may also be ligated for wounds, resection of the upper jaw, hemorrhage from the tonsils, and angiomatous growths affecting the region which it supplies.
Unlike some other arteries the external carotid sometimes seems to have no trunk, consisting almost entirely of branches. Therefore in ligating it one should not expect to find a big artery the size of the internal carotid, but often one only half as large. The branches of the external carotid artery are the superior thyroid, lingual, and facial, which proceed anteriorly toward the median line; the occipital and posterior auricular, which supply the posterior parts; the ascending pharyngeal, which comes off from its deep surface and ascends to the base of the skull; and the temporal and internal maxillary arteries, which are terminal. It is ligated either near its commencement just above the superior thyroid artery or behind the angle of the jaw above the digastric muscle.
At its commencement at the upper border of the thyroid cartilage the artery is quite superficial, being covered by the skin, superficial fascia, platysma, deep fascia, and overlying edge of the sternomastoid muscle. It is to be reached through an incision 5 cm. in length along the anterior edge of the sternomastoid muscle in a line from the sternoclavicular joint to midway between the angle of the jaw and the mastoid process. The middle of the incision is to be opposite the thyrohyoid membrane. The bifurcation of the common carotid artery is an important landmark.
The superior thyroid artery is given off at the very commencement and sometimes even comes from the common carotid just below. The ascending pharyngeal is the next branch, about 1 cm. above the superior thyroid. It comes off from the deep surface of the artery; almost opposite to it and in front is the lingual. It will thus be seen that the distance between the lingual and the superior thyroid, where the ligature is to be placed, is quite small. The superior thyroid is about opposite the upper border of the thyroid cartilage, while the lingual is opposite the hyoid bone. Beneath the artery is the superior laryngeal nerve, but it is not liable to be caught up by the needle in passing the ligature because it lies flat on the constrictors of the pharynx and is apt to be a little above the site of ligation.
The veins are the only structures liable to cause trouble. They are superficial to the arteries. On account of their irregularity more may be encountered than is expected. The superior thyroid and lingual veins both cross the artery to empty into the internal jugular. The facial vein is also liable to be met, as the facial artery frequently springs from a common trunk with the lingual. The communicating branch between the facial and external jugular vein is another one that should be anticipated. These veins, when it is possible, are to be hooked aside; otherwise they are to be ligated and cut. Great care should be taken not to mistake a vein for the artery. It might appear an easy matter to readily recognize the artery and distinguish between it and the veins, but this is not always the case in the living subject. The veins may have some pulsation transmitted to them from the adjacent arteries and the artery may temporarily have its pulsations stopped by pressure from the retractors. The living artery touched by the finger seems soft and does not give the hard, resisting impression felt in palpating the radial in feeling the pulse. The difference in thickness of the coats is also sometimes not apparent at a first glance.
The ligature is to be passed from without inward so as to guard against wounding the internal carotid.