Thursday, December 16, 2021

THE HEAD AND NECK CONTINUED  

    All of these movements are performed to position the head, which itself should be seen at two units: the face and the braincase. The face of the skull is a bony shield that hangs down from the rounded braincase. It is perforated by several holes that provide receptacles for the sense organs, the connection between the outside world and the brain. The eyes of the human and of most primates are on the front of the face rather than on the side as they are in most mammals. The two eyes, spaced a short distance apart, see things from two different perspectives. The combined information from these two points of view is simultaneously processed by the brain, allowing for the judging of distances. The sense organs need to be protected. The eyes are set in to the skull with prominent ridges of bone above and below them. The muscle fibers of the eyelid that are arranged around the eye are in concentric circular configuration. These muscles are tethered to the skull near the nose by a small tendon that you can feel as a small lump on the inner corner of the eye. The muscles of the lips are in a thicker, but similar circuit of muscles that when contracted as a whole, cause the lips to pucker. These muscles can also be contracted in part. Covering the opening on the skull for the organs of the sense of smell is a “tent” made of three sections of cartilage. The human nose is unusual in how it juts out from the face. Some paleo-anthropologists speculate that the prominent nose arose as a means of warming up air as it was inhaled, preventing the brain from getting too cold. 

 



The major bony structures of the face are attachments for the most powerful muscle of the head, the muscles for chewing and biting. The delicate edge of the temple, which you can feel on the side of the head by the eye, and continues as a long graceful arch on the side of the skull, is the origin of the temporal muscle. The thin, fan shaped temporal muscle points down towards the lower jaw, into which it is inserted. This insertion is hidden from sight and touch because it occurs under the arc of bone that extends from beneath the eye to the ear. This is the zygomatic arch, or cheekbone. It is the origin of the most significant facial muscle - the masseter. The masseter is connected to the bottom edge of the zygomatic arch and descends diagonally to be inserted near the corner of the lower jaw. Once you know the front edge of the masseter is there you can discern it in even the most full cheeked subject. For the drafts-person the distance between the eye and the ear can sometimes seem like the greatest distance in the body - an empty zone with little contour. An understanding of the zygomatic arch and the masseter provides landmarks for the artist's eye in traveling this distance. 




In our evolutionary development, intelligence combined with social existence made articulate speech a possible advantage. But in apes even with the reduction in size of the lower jaw, a bony shelf that reinforced the u-shape of this structure still made clear speech difficult. The solution to this was a misplacement of this buttress of bone into a knob of bone into the front of the jaw, the chin. This was a very late arrival in our skeletal structure and we must imagine our ancestors as folks with few words. 





Friday, December 10, 2021

THE NECK AND PROPORTIONS OF THE HEAD

 The  Neck




Primarily responsible for holding the head up is the nuchal ligament. This ligament is connected to the back of the head and all seven vertebrae of the neck. It functions as the cable that pulls the weight of the head back. A ligament serves the function of holding the head up well: it is strong and flexible and unlike a muscle, does not tire. Like all ligaments and tendons it does not have the power of self motion. 


The muscles of the neck are responsible for the positioning of the head, which can tip forward and back and to which side, and can turn right and left. 


The Backward tip of the head is accomplished by the trapezius, which is inserted into the base of the skull. When the cervical or neck position of the trapezius contracts, it pulls the back of the head downward. To tip the head forward, since the head is balanced toward the front, all that is usually necessary is for the trapezius to relax and gravity will pull the head down. But, if there is resistance, for example if one is lying on their back, we must act against gravity. Here a pair of muscles comes into play: the sterno-clio-mastoid muscles. Each is attached to either side of the head just behind the ear to a bony lump called the mastoid process. They then descend the column of the neck to attach to the sternum via a prominent cylindrical tendon and to the clavicle via a less obvious flat tendon. Pulling the chin toward the chest is accomplished by the interaction of both sterno-clio-mastoid muscles. To rotate the head only one of them contracts, pulling the back of the head toward the contracting side and the chin away from it. 


The rotations of the head from left to right bear close examination. Looking at yourself in the mirror with your neck and shoulders exposed, turn your neck to the left. In doing so place both your fingertips on your sterno-clio mastoid muscles and feel the muscle bulge as it contracts. You will notice as you turn to the left it is the right side that is contracting and as you turn to the right side it is the left. The sterno-clio mastoid is a diagonal muscle that links the front of the chest to the back of the skull. When it contracts the muscle pulls the ear towards the front of the chest. Thus the diagonal sterno-clio mastoid is repositioned to be vertical above the front of the chest. 


Between the two sterno-clio mastoids are the larynx and the trachea connecting the nose and mouth to the lungs.Lower down the cartilaginous trachea is partially obscured by the thyroid gland. Between the sides of this V, the larynx emerges, slanting forward towards the chin. Keeping the slant from being a straight diagonal is the hybrid bone, which is strung under the chin a the top front of the neck which pulls the tissues there. Tipping the head from side to side is performed by one side of the trapezius in the neck acting in conjunction with the sterno-clio mastoid of the same side. 













 

  

THE HEAD AND NECK CONTINUED        All of these movements are performed to position the head, which itself should be seen at two units: the ...