About the usefulness of the neck and the anatomy of its skeleton

The neck was created for the sake of the pulmonary tube, and the pulmonary tube was created for the sake of utilities, which we will mention in its place. Since the cervical and generally upper vertebrae are carried by the part of the spine located under them, they must necessarily be smaller. After all, what is carried must be lighter than what is carried if movements are to be performed in perfect order. Since the beginning of the spinal cord, like the beginning of the canal, should be thicker and larger, because the upper part of it received a larger part of the nerves than the lower one, the openings of the cervical vertebrae should be wider. But the small size and large width of the cavity contribute to the thinning of the vertebrae; Therefore, they must have a certain degree of strength, which would compensate for their weakening from the two mentioned reasons. That is why it was necessary to create them the strongest of all vertebrae. Since the body of each of these vertebrae is thin, the spines on them are created small; after all, if they were created large, then the vertebra would be prone to fracture and damage when the spikes hit strong objects. But since the spikes on them are small, their wings are made large and have double ends. Since their need for mobility is greater than the need for stability, because they do not bear many bones on themselves, like the vertebrae located below, the joints of the cervical vertebrae are more pliable compared to the joints of the vertebrae located below them. The strength that they lack due to pliability is compensated to the same or greater extent by the nerves, muscles and vessels that surround them and pass through them. This eliminates the need to increase joint strength. Since there is little need to strongly strengthen the joints of these vertebrae and their degree of strength is sufficient for their work, their articulating processes, directed upward and downward, are not created as large and wide as those of those vertebrae that are below the neck. On the contrary, their lower part is made longer, and their ligaments are more pliable. The place where their nerves exit is created common to two vertebrae, as we mentioned above, for each cervical vertebra, due to its thinness, small size and width of the passage for the spinal cord, cannot have a special opening; The exception is those vertebrae, which we will talk about later and outline their structure specifically.

Now we will say that there are seven cervical vertebrae: this number is proportionate to the number and length

vertebrae Each of these vertebrae, except the first, has all the eleven processes mentioned: one spine, two wings, four articulating processes directed downward. Each wing has two branches; the round opening for the exit of the nerve is divided in half between each two vertebrae. However, the first and second vertebrae have features that the others do not. First of all, you should know that movements of the head to the right and left are carried out by the joint between the head and the first vertebra, and movements forward and backward are carried out by the joint between the head and the second vertebra. First we should talk about the first joint. We will say that on the two protrusions of the first vertebra, directed upward and on both sides of the vertebra, two pits are created into which two processes of the head bone enter. When one of them rises and the other descends, the head tilts towards the descending process. The second joint cannot be located on the same vertebra, and a special vertebra was created for it, namely the second. On its front side, facing inward, a long hard process is created that extends beyond the second vertebra and passes through the foramen of the first vertebra in front of the spinal cord. This hole is common to both vertebrae. It, that is, the hole, is longer from back to front than from right to left, and this is because two bodies pass through it in front and behind, which take up more space than one. As for the size in width, it corresponds to the size of the larger of the passing bodies, that is, the spinal cord. This process is called a “tooth”. The spinal cord is separated from it by strong ligaments, which are created in order to delimit the area of ​​the “tooth” and the area of ​​the spinal cord, so that the “tooth” does not damage the spinal cord during movement and does not put pressure on it. This process rises from the first vertebra and enters the fossa of the head bone, so that the fossa of the head bone rotates on it from back to front. This “tooth” grows forward for two benefits. One of them is that it is safer for him, and the second is that the thinner side of the vertebra is on the inside, and not on the outside.

The peculiarity of the first vertebra is that it does not have a thorn, so that the thorn does not burden the vertebra and so that the vertebra is not damaged because of it. After all, the same process that pushes away what is stronger than it causes fracture and damage to what is weaker. There is also no thorn so that it does not damage the numerous muscles and nerves around it. At the same time, the need for a protective spike here is small, because the first vertebra is, as it were, buried and hidden among all sorts of protections from various damages. As a result of all these circumstances, it is deprived of wings, especially since most of the nerves and muscles are located on both sides of this vertebra, and are closely located, for it is close to their origin, so that there is no room for wings.

One of the features of the first vertebra is that the nerve emerging from it does not emerge from the side and not from a foramen common to the two vertebrae, but from two foramina located near its upper edges towards the back. The fact is that if the exit of the nerve were located where the processes of the head bone meet and where they make strong movements, this would cause significant harm to the nerve. The same would happen if the exit of the nerve was at the articulation of the second vertebra: it has two processes that enter the foramen of the second vertebra through a flexible articulation that moves back and forth. It is also not suitable, for the reasons mentioned when describing the structure of other vertebrae, for the nerve to exit from the front, back or sides, since the bone there is thin due to the presence of a “tooth”. Therefore, the exit of the nerve must inevitably be located slightly below the articulation of the head, beyond the edges, that is, in the middle, between the back and the edge.

Consequently, it is necessary that both openings be small, and it is equally necessary that the nerves be thin.

As for the second vertebra, the exit point of the nerve cannot be at its top, as is possible for that vertebra, for if the exit of the nerve were in the same place as at the first vertebra, one would be afraid that the movements of the first vertebra when tilting the head forward or backward will crush or cause pain to the nerve. For the same reason, it is impossible for the nerve to exit from the front, back or sides; in this case, it would be common with the first vertebra, and the nerve growing from it would necessarily have to be thin and would not compensate for the deficiency of the first nerve. The result would be pairs of weak nerves connected together. This hole would then also be common to the first and second vertebrae, and for you the justification is already clear that the first vertebra would suffer if it had holes on both sides. Therefore, it is necessary that the opening of the second vertebra be located on both sides of the spine, opposite the openings of the first vertebra, so that the body of the first vertebra can participate in the formation of the common opening.

The spine growing from the second vertebra is connected to the first vertebra by a strong ligament.

The articulation of the skull with the first vertebra and the articulation of the skull and the first vertebra with the second vertebra are more pliable than other articulations of the vertebrae, since these articulations experience a greater need for movement, and their movements must be sufficient in scope and obvious. When the head moves with the articulation of one of the two vertebrae, the other remains motionless in its second articulation, as something one with it; thus, if the head moves forward or backward, it forms, as it were, one bone with the first vertebra, and when it moves to the side, without tilting, then the first and second vertebrae form, as it were, one bone. This is what we have to say about the cervical vertebrae and their features.