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.
On viewing the neck from the side the prominent sternocleidomastoid muscle with its thick anterior and thin posterior edge is seen to divide it into two spaces, an anterior and a posterior. They are called the anterior and posterior cervical triangles.
The anterior cervical triangle has for its anterior side the median line of the neck. Its posterior side is the anterior edge of the sternomastoid muscle. Its upper side is the lower edge of the mandible from the symphysis to the angle and thence across to the mastoid process. The anterior triangle is further divided into the space above the digastric muscle called the submaxillary triangle, - from its containing the gland of that name, - the superior carotid triangle above the anterior belly of the omohyoid muscle, and the inferior carotid triangle below the omohyoid muscle.
The submaxilliary triangle is so called from its containing the submaxillary gland. It is also sometimes called the lingual triangle, from the lingual artery. It has as its upper side the lower edge of the mandible from near its symphysis around the lower edge of the body to the ramus and thence in a straight line across to the mastoid process. Its anterior side is the anterior belly and its posterior side is the posterior belly of the digastric muscle. The submaxillary gland can usually be felt beneath the jaw. Beneath it runs the facial artery to pass over the body of the mandible in front of the anterior edge of the masseter muscle. The gland lies on the hyoglossus and mylohyoid muscles, which form the floor of this triangle. It is encased in a sort of pocket formed by a splitting of the deep cervical fascia. The posterior portion of this fascia runs from the styloid process to the hyoid bone and is called the stylohyoid ligament.
Lymphatic nodes lie on the submaxillary gland and in carcinomatous disease they become enlarged and then can be readily palpated. In operating on these lymphatic nodes for tuberculous disease, care should be taken to distinguish between them and the submaxillary gland. The tendon of the digastric muscle does not come clear down to the hyoid bone but the loop which binds the two together is sometimes a centimetre or more in length. The lingual artery enters the sub- . maxillary triangle near the apex of the angle formed by the tendon of the digastric. It crosses beneath the posterior belly of the digastric muscle and, particularly if the digastric muscles contract, it may lie close to the tendon. Frequently the search for it is made too high in the triangle and too far away from the hyoid bone. When the submaxillary gland is lifted from its bed the hypoglossal nerve is seen beneath lying on the hyoglossus muscle. The lingual artery lies beneath the hyoglossus muscle and the muscle is cut through in order to find it. The submaxillary region is the seat of Ludwig's angina, a septic inflammation involving the cellular tissues beneath the tongue and jaw around the submaxillary gland and the upper portion of the neck. It is a dangerous affection and may cause death not only by sepsis but also by oedema of the larynx.
Fig. 164. - Deeper structures of the submaxillary region, especially the vessels.
Dr. T. Turner Thomas (Annals of Surgery, February and March, 1908), has pointed out that the infection passes from the inside of the mouth to the submaxillary region outside by following the connective tissue around the submaxillary gland as it winds around the posterior edge of the mylohyoid muscle through the opening existing between this muscle in front and the anterior portion of the middle constrictor of the pharynx behind.
The superior carotid triangle is limited posteriorly by the sternomastoid muscle, superiorly by the posterior belly of the digastric, and inferiorly by the anterior belly of the omohyoid. The location of the omohyoid muscle can be determined by that of the cricoid cartilage, as the muscle crosses the common carotid artery about opposite that point. The sternomastoid muscle can be both seen and felt. It is attached above from the apex of the mastoid process to the middle of the superior curved line on the occipital bone. It is attached below by a sternal head to the upper anterior part of the first piece of the sternum, and by a clavicular head to the inner third of the clavicle on its superior and interior border. Its action will be mentioned in discussing wry-neck.
Fig. 165. - Submaxillary region. The anterior portion of the submaxillary gland is seen winding around and beneath the posterior edge of the mylohyoid muscle. The posterior portion of the gland has been cut away. The posterior belly of the digastric and the stylohyoid muscles have also been removed.