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 neck supports the head. It is a pedestal for the head, and is long in proportion to its thickness; the apparent object of this being to elevate the head and allow it to be moved freely in different directions. The animal is thus better enabled to discover its enemies and to guard itself against them.
The various structures of the neck are mostly long, running between the head above and the trunk below. This is the case with the spine, the air- and food-passages, the blood-vessels, nerves, and even some muscles, as the sternomastoid and trapezius. The shorter structures are either the component parts of the longer ones, as the vertebrae of the spine and the rings of the trachea, or are separate organs like the larynx, thyroid, and submaxillary glands. The presence of these latter organs is not dependent on the length of the neck as is that of the others. In the frog, which practically has no neck, the head being placed directly on the trunk, there still exist both larynx and thyroid gland. In the singing birds the vocal organ or syrinx is placed in the chest at the bifurcation of the trachea. As regards the cervical spine, blood-vessels, air- and food-passages, and muscles, these evidently are proportionate to the length of the neck. In the batrachians or frogs there is but a single cervical vertebra; in the swan there are twenty-five cervical vertebrae, and in the fishes none. In man of course the number of cervical vertebrae remains the same, seven, no matter what the length of the neck. From a consideration of these facts we may perhaps state that the neck itself is a subsidiary organ, not of any great importance in itself, but rather in relation to some other portion of the body - that portion being the head. It is the staff which supports the head by means of the cervical spine and muscles.
The neck contains the great currents of blood which pass to and fro between the head and trunk. It carries the air- and food-passages, which run from the mouth above to the lungs and stomach below, and incidentally it contains the larynx, the thyroid and submaxillary glands, and some lymphatic nodes. The cerebrospinal nerves of all the body below the head pass either into the neck or through it to the parts beyond. From these facts it becomes evident that, while the neck in itself may be a subsidiary organ, for our purposes it is of the greatest importance, because interference with its structure either by disease or injury - operative or accidental - may destroy the brain above, by interfering with its nourishment, or the body below, by interfering with the vital functions of respiration and nutrition, or may paralyze it by destroying the conductivity of its nerves. The construction of the neck then should be studied with a view of explaining or understanding the diseases and injuries of its various parts and the operations performed for their relief.
Owing to its exposed position the neck is frequently injured by sprains, contusions, cuts, and punctured, gunshot, and all sorts of wounds. The cervical spine may become dislocated or fractured and is frequently the seat of caries. The muscles become contracted, producing torticollis or wry-neck. They may sometimes be ruptured, as in childbirth.
The arteries are affected with aneurism, necessitating their ligation. They are also divided in cut-throat cases and wounds. The veins are of importance in almost every operation; bleeding from them is dangerous and may be difficult to control.
The lymphatic nodes are more numerous than elsewhere in the body. Frequently they are the seat of tuberculous or sarcomatous enlargement, necessitating their removal. They may break down and produce wide-spreading and dangerovis abscesses, which are guided in their course by the fascias; hence a knowledge of the construction of the deep fascias of the neck enables us to understand them.
The submaxillary and thyroid glands are the seat of enlargement and foreign growths requiring the performance of extensive operations for their extirpation. Enlargement of the thyroid gland constitutes the disease known as goitre. It is also involved in exophthalmic goitre or Graves' s or Basedow's disease.
The skin and subcutaneous tissue become the seat of inflammation and cellulitis. In cases of wounds this cellular inflammation may involve the structures beneath the deep fascia; this occurs in cut-throat and gunshot wounds.
The neck is also liable to other affections, such as cysts due to embryological defects. Large cysts are formed called hygromas, also sinuses or fistulae, the congenital fistula of the neck. The larynx may be the seat of malignant disease; hence its removal is undertaken. The operations of tracheotomy, laryngotomy, and oesoph-agotomy are also at times necessary. In order to understand these various affections and procedures one must be familiar with the construction of the neck, what composes it, where the various structures lie and their relation to one another. In order to utilize this knowledge we must be able to recognize and identify the position of various structures before the skin is incised, for it is rarely that a case presents itself with a wound that permits a view of the deeper structures; hence the importance of a thorough knowledge of its surface and the structures capable of being recognized through the skin.