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 veins found in and near the superior carotid triangle are the anterior and internal jugulars and their branches. A small portion of the commencement of the external jugular may also be in its extreme upper angle.
The anterior jugular vein begins just above the hyoid bone from veins in the submaxillary and submental regions. It lies on the deep fascia and passes down the neck about 1 cm. from the median line, then just above the sternum it turns down and out under the sternomastoid muscle to empty into the external jugular or subclavian. At the point of turning it sends off a branch across the median line to the vein on the opposite side. Thus the blood-current can pass directly across the neck from one external jugular vein to the other. Sometimes there is another communication between the two anterior jugulars through a small branch crossing just above or excised in operations for enlarged lymph-nodes'or for infective thrombus. It is not so large above the facial vein as below that point. It becomes so involved in enlargements of both tuberculous and carcinomatous lymph-nodes that it may be necessary to excise it along with the tumor. Its removal does not give rise to any serious svmptoms.
Fig. 168. - Dissection of the deep structures of the front of the neck.
It becomes thrombosed by the extension of a thrombus from the transverse (lateral) sinus, which in turn becomes affected by the extension of suppurative middle-ear disease through the medium of caries of the bones. When the internal jugular is thrombosed it is evidenced by swelling, redness, and tenderness along the anterior border of the sternomastoid muscle just behind the angle of the jaw. Bleeding from the veins in this region is particularly dangerous because the internal jugular itself is so large and having no valves, will bleed both from the side towards the heart and that towards the head.
The veins also, which are tributary to it in this region, are so large and are wounded so close to the main trunk that the blood from the internal jugular itself regurgitates. The walls of the veins are thin and, if the fascias happen to be relaxed, fall readily together and thus are difficult to see, and are so adherent to the fascias as not to be readily seized. The surgery of this region requires extreme care and the avoidance of haste.
Lying between the internal jugular vein and the internal and common carotid arteries is the pnetimogastric or tenth nerve. It here gives off the superior laryngeal nerve, the internal branch of which enters the larynx through the thyrohyoid membrane to endow the interior of the larynx with sensation; the external branch goes to supply the cricothyroid muscle. The pneumogastric nerve is frequently seen in operations in this region. Its division has not been fatal.
The hypoglossal nerve winds around the occipital artery and goes forward on the hyoglossus muscle, which separates it from the lingual artery. The descendens hypo-glossi filament leaves the parent nerve as it winds around the occipital artery. It lies on the carotid artery in the form of a loop formed by the addition of branches from the second and third cervical nerves. As it descends on the sheath of the vessels it gives a branch to the anterior belly of the omohyoid muscle. The loop sends branches to the sternohyoid, sternothyroid, and posterior belly of the omohyoid, and if the nerve is divided paralysis of these muscles will occur. The nerve is to be pushed aside when ligating the artery and not included in the ligature. The superficial branches from the cervical plexus which come from the middle of the posterior edge of the sternomastoid muscle and ramify towards the median line, are nerves of sensation, and their division in operative work causes no serious symptoms, hence they are disregarded. The inframaxillary branches of the seventh or facial nerve supply the platysma.