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 superior thyroid is the first branch of the external carotid and is given off close down to the bifurcation or even from the common carotid itself just below. It lies quite superficial but of course beneath the deep fascia. At first it inclines upward and then makes a bend and goes downward to the thyroid gland. It gives off three comparatively small branches, the hyoid along the lower border of the hyoid bone, the sternomastoid to the muscle of that name, and the superior laryngeal to the interior of the larynx. The larger portion of the artery goes downward to supply the thyroid gland and muscles over it, therefore the artery is to be looked for at the upper edge of the thyroid cartilage, and not near the hyoid bone. The incision is the same as for ligating the external carotid low down, viz., 5 cm. along the anterior edge of the sternomastoid muscle, its middle being opposite the upper edge of the thyroid cartilage. Veins from the thyroid gland - superior thyroid - will probably cover it. After the deep fascia has been opened, the external carotid is to be recognized at its origin from the common carotid and then the superior thyroid artery found and followed out from that point. The ligature is to be passed from above downward to avoid the superior laryngeal nerve. This nerve lies distinctly above the artery and is not liable to be injured if the thyroid artery is followed out from its origin at the external carotid. Treves suggests ligating it between the sternomastoid and superior laryngeal branches, but it is more readily reached closer to the external carotid artery. Ligation of the Lingual Artery. - The lingual artery may be ligated for wounds, as a preliminary step to excision of the tongue, and to check the growth of or bleeding from malignant growths of the tongue, mouth, or lower jaw.
The lingual artery springs from the external carotid opposite the hyoid bone about 1 cm. above the bifurcation of the common carotid. It is composed of three parts: the first, from its point of origin to the posterior edge of the hyoglossus muscle; the second, the part beneath the hyoglossus muscle; and the third, the part beyond this muscle to the tip of the tongue.
The artery is usually ligated beneath the hyoglossus muscle in the second part of its course, although it is sometimes desirable to ligate it in the first part of its course.
The first part inclines upward and forward, above the greater horn of the hyoid bone, to the hyoglossus muscle, beneath which it passes in a direction somewhat parallel to the upper edge of the hyoid bone. It lies on the middle constrictor of the pharynx and superior larnygeal nerve and is covered by the skin, platysma, and fascia. It lies immediately below the stylohyoid and digastric muscles and is crossed by the hypoglossal nerve and some veins. This portion frequently gives off a hyoid branch which runs above the hyoid bone. It is often missing, in which case the parts are supplied by the hyoid branch of the superior thyroid. From either the end of the first part or the beginning of the second part, the dorsalis linguae branch arises.
The second part of the lingual lies on the superior constrictor and geniohyoglos-sus muscles and is covered by the hyoglossus. It runs in a direction somewhat parallel to the upper edge of the hyoid bone and from 0.5 to 1 cm. above it. In this
Fig. 174. - Ligation of the lingual arterypart of its course it is usually accompanied by one or two veins and the hypoglossal nerve is superficial to it, the hyoglossus muscle separating them. This is the part of the artery chosen for ligation. An incision is made, convex downward, running from below and to one side of the symphysis nearly down to the hyoid bone and then sloping upward and back, stopping short of the line of the facial artery, which can be determined by the groove on the mandible just in front of the masseter muscle. The skin, superficial fascia, and platysma having been raised, the submaxillary gland is seen covered with a comparatively thin deep fascia. Some veins coming from the submental region may then be encountered. They may be ligated and divided. The submaxillary gland is next to be lifted from its bed and turned upward against the mandible, carrying with it the facial artery, which is adherent to its under surface. The tendon of the digastric will now be seen with the anterior and posterior bellies of the muscle forming an angle with its point toward the hyoid bone. These with the hypoglossal nerve form what has been called the triangle of Lesser. It is in this space that the artery is ligated. The floor of the space posteriorly is formed by the hyoglossus muscle, while anteriorly is seen the edge of the mylohyoid muscle. Through the thin fascia overlying the hyoglossus muscle can be seen the hypoglossal nerve, and below it, sometimes a vein. The artery lies under the muscle, while the veins may be either on or under the muscle or both.
The apex of the angle formed by the tendon of the digastric muscle is held down to the hyoid bone by a slip of fascia which is an expansion of the central tendon of the muscle and the tendon of the stylohyoid muscle. The distance at which the central tendon of the digastric is held away from the hyoid bone varies in different individuals and is an important fact to bear in mind in searching for the artery. If the tendon rests high above the hyoid bone the artery must be looked for low down, sometimes even under the tendon; if, on the contrary, the tendon is low down the artery may be o.5 to 1 cm. higher up. The hypoglossal nerve lies on the muscle and nearer to the mandible than the artery. If there is a vein on the hyoglossus muscle it is apt to be below the nerve, that is, nearer the hyoid bone, and may lie directly over the artery. The vein and the nerve are to be displaced up towards the jaw and an incision a centimetre long made through the hyoglossus muscle a short distance above the digastric tendon and parallel with the hyoid bone. This incision should not be deep, as the muscle is only 2 or 3 mm. (1/8 in.) thick.
Fig. 175. - Ligation of the subclavian artery.
The edges of the incision being raised and displaced upward and downward, the artery will probably be seen running at right angles to the fibres of the muscle and parallel to the hyoid bone. If not seen at once it should be looked for below the incision, nearer to the hyoid bone. Care must be taken not to mistake the vein for the artery. That this is not an unlikely thing is shown by its occurring in the hands of a distinguished surgeon who had had exceptional experience in this same operation. The ligature needle may be passed from above downward to avoid including the hypoglossal nerve. Subclavian Artery. - The right subclavian artery runs from the sternoclavicular articulation in a curved line to the middle of the clavicle. It rises 1.25 cm. (1/2 in., Walsham) above the clavicle. The innominate bifurcates opposite the right sternoclavicular joint. The left subclavian springs directly from the arch of the aorta, therefore it is longer than the right by 4 to 5 cm., this being the length of the innominate. As the subclavian artery passes outward it is crossed by the scalenus anticus muscle, which divides it into three parts: the first part, extending to the inner side of the muscle, gives off three branches, the vertebral, internal mammary, and thyroid axis; the second part, behind the muscle, gives off the superior intercostal; the third part has no branches.
The first portion of the subclavian lies very deep and operations on it have been so unsuccessful that they have been practically abandoned. As it is frequently involved in aneurisms its relations are worth studying. In approaching the artery from the surface it is seen to be covered by the sternomastoid, the sternohyoid, and the sternothyroid muscles. The outer edge of the sternomastoid muscle corresponds with the outer edge of the scalenus anticus. The three first-named muscles having been raised, the artery is seen to be crossed by the internal jugular, the vertebral, and perhaps the anterior jugular veins. The anterior jugular above the clavicle dips beneath the inner edge of the sternomastoid muscle to pass outward and empty into the external jugular or subclavian. The pneumogastric nerve crosses the artery just to the inner side of the internal jugular vein. Below, the artery rests on the pleura, and on the right side the recurrent laryngeal nerve winds around it. Behind the artery are the pleura and lung, which rise somewhat higher in the neck than does the artery.
On the left side the phrenic nerve leaves the scalenus anticus muscle at the first rib, crosses the subclavian at its inner edge, and passes down on the pleura to cross the arch of the aorta. To the inner side of the artery runs the thoracic duct, which, as it reaches the upper portion of the artery, curves over it to cross the scalenus anticus muscle and empty into the junction of the internal jugular and subclavian veins. The trachea and oesophagus are likewise seen to the inner side of the artery. The thyroid axis comes off its anterior surface, the vertebral from its posterior, and the internal mammary below.
The second portion of the subclavian artery lies behind the anterior scalene muscle. In front of the anterior scalene is the subclavian vein. The phrenic nerve runs on the muscle and at the first rib leaves it to continue down between the right innominate vein and pleura. Behind and below, the artery rests on the pleura and the middle scalene muscle is to its outer side. Thus it is seen that the artery passes through a chink formed by the anterior scalene muscle in front and the middle scalene behind. They both insert into the first rib. The posterior scalene is farther back and inserts into the second rib. Above the artery are all the cords of the brachial plexus. One branch of the subclavian, the superior intercostal artery, is given off near the inner edge of the anterior scalene muscle.
The third portion of the subclavian runs from the outer edge of the anterior scalene muscle to the lower border of the first rib. This part of the artery is the most superficial. The only muscle covering it above is the thin sheet of the platysma, lower down the subclavius muscle and clavicle overlie it; but the operations on the vessel are done above these structures, hence they do not interfere. There are apt to be a number of veins in front of the artery. The external jugular and transverse cervical veins are certain to be present and perhaps the suprascapular and cephalic, which may enter above instead of below the clavicle. These veins may form a regular network in the posterior cervical triangle above the clavicle and prove very troublesome. Above is the brachial plexus and transverse cervical artery and still higher is seen the omohyoid muscle. The suprascapular artery is lower down and usually concealed just below the upper edge of the clavicle. The lowest cord of the brachial plexus, formed by the first dorsal and last cervical nerves, may be posterior to the artery. The nerve to the subclavius muscle passes down in front of it.