İKİNCİ FEN · ÜÇÜNCÜ BÂB · BİRİNCİ FASIL · Beşinci Madde
Fifth Article
Concerning the movements and muscles of the head and neck.
Know, O esteemed one, that anatomists have stated: The head possesses both movements specific to itself and shared movements with the five vertebrae of the neck, whereby the neck participates in the inclination of the head; these two types of movement are distinct and joint. [Whether it be the movement unique to the head or the common movement between it and the neck,] the head either bends forward and backward, or turns from side to side. In some instances, muscles rotate the head, causing a circular motion.
There are two muscles that enable the specific bending movement of the head, originating from its sides. For their fibers emerge from behind the ear above and below from beneath the sternum, uniting as one entity with their fibers at the upper portion behind the ear, and then proceed to [the] head. Thus, if only one of these moves, the head inclines towards that side. And if both move together, the head bends forward in a balanced manner. The muscles that bend the head along with the neck are a pair situated behind the esophagus. They reach and join the first and second vertebrae. If the muscle near the esophagus contracts, only the head bends. If the muscle joining to the vertebrae contracts, the neck also bends forward. There are four pairs of muscles that bend and rotate the head solely backward. The first pair is concealed beneath those described above. The origin of these pairs is found above the joint between the head and neck. Another pair lies on either side of the first vertebra. A third reaches the spinal process of the second vertebra, its function being to maintain the head’s straightness during bending [123/a]. The fourth pair originates above them, sloping down from beneath the third muscle pair, passing over the top and reaching the side of the first vertebra. The first two pairs rotate the head backward without tilting it to either side. The third pair maintains the head's straightness. The fourth pair rotates the head backward upon its socket.
There are four pairs of muscles that bend the head backward along with the neck; three pairs of them are concealed beneath and enveloped by the fourth. Each of the fourth pair is triangular in shape, with the base of the triangle being the posterior bone of the brain, descending into the nape (neck). Beneath it lie the aforementioned three pairs, one descending on either side of the cervical vertebrae, another inclining considerably to the sides, and a third encompassing the sides around the vertebrae. There are two pairs of muscles that tilt the head from side to side; they attach to the head joint. The location of one pair is towards the front; one muscle terminates between the head and the second vertebra on the right side, while the other terminates on the left side. The location of the second pair is towards the back; one muscle terminates between the head and the first vertebra on the right side, and another joins a joint on the left side.
Thus, whichever of these four muscles contracts, the head turns directly toward that side. If any two of them contract together from one side, the head inclines directly towards them. And if all four move together, the head remains upright in a straight position. These four muscles are the smallest among the others, but due to their proximity and orderly arrangement beneath the other muscles, they perform the functions of larger muscles.