dcorc
03-06-2005, 10:57 AM
While the previous classrooms in the series have mainly taken the form of practical demos, I wanted to do something slightly different in this one. Of course it's impossible to teach "all about" head and neck anatomy across a fortnight, and I doubt anyone here would really like to learn it either! But it's certainly easy when looking at portraits to tell the difference between those people who have a fair understanding of anatomy, and those who do not. So what I want to do here is to try to help people to think in terms of anatomical structure when they do portraits.
I'll introduce various topics with additional posts in the course of the 2 week period, (building up information gradually, starting with some basics on the bones), suggest some study exercises, and (hopefully!) answer any questions. I'm particularly keen to point out features which vary with age, sex and ethnicity, as careful attention to these can all help the portraitist achieve a likeness (and give control over the issue of accurate versus flattering!). I'd also like to try to shed a little light on how some of the structural features - for example the structure of the skin and underlying tissues - affect surface appearance. Understanding these factors may help you make someone look younger (or older), fatter or slimmer, for example.
Let's start today with some bony anatomy:
the skull consists of 3 areas
1.the cranial vault, or calvaria enclosing the brain, and
2.the facial skeleton, including the upper jaw (maxilla)
3.the lower jaw (mandible)
These two diagrams show the various bones which make up the skull, colour-coded to make it easier to see how they all fit together.
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-skullfront.jpg http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-skullside.jpg
and here's that side view again, this time with the bones named:
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-skullnames.jpg
Have a look at this pair of casts of skulls - the left hand one is an adult, and the other is a 5 year old - note the difference in relative proportions of the cranial vault versus facial skeleton
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-adultskull.jpg http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-5yrold.jpg
- in the child the facial skeleton is a smaller proportion of the total head, though the orbits are large, as eyes are proportionately larger in children than in adults - and note how there is vertical elongation of the midfacial skeleton in the adult, particularly of the maxilla and zygomatic bones, and of the mandible - this occurs during the teens, and is a factor in the rapidly changing facial appearance during adolescence. Note also the difference between the adult permanent teeth, and the childhood deciduous dentition.
The maxilla is part of the cranium, and the upper teeth are inserted into it - thus their position is rigidly set in relation to the rest of the cranium.
Let's remove the mandible, and look at the skull-base from below:
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-skullbase.jpg
Notice how the majority of the hard palate behind the teeth of the upper jaw is maxilla, and behind this is the palatine bone (here, centrally, in pale pink) - the back edge of that is the attachment of the tissues of the soft palate - above that is the posterior entrance to the nasopharynx.
Note that much of the central skull base area is the sphenoid bone (here in grey), and posterior to it is the occipital bone (in yellow). The large hole in the occipital bone is the foramen magnum through which the spinal cord passes. In humans, the foramen magnum faces inferiorly (i.e. downwards) associated with our upright stance, whereas in most animals the foramen magnum opens posteriorly (backwards). To either side of the foramen magnum, we can see the articular condyles - the surfaces that the first cervical vertebra hinges on. ( We have 7 cervical vertebrae in the neck, between the base of the skull above, and, below, the first thoracic vertebra - which has the first rib attached).
I'd like to turn our attention to the jaw for a while, and its relationships.
Let's look at the hinge area:
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-tmjbones.jpg
If we look at the temporal bone from the side, we can see the auditory meatus - this is where the external ear canal links up to the middle ear - immediately anterior (in front of this) is the temporomandibular joint, between the head of the mandible, and the lower and most posterior part of the zygomatic arch (which in turn forms the bony prominence of the cheek).
Behind the auditory meatus is the mastoid process, where the sternocleidomastoid muscle of the neck attaches (this is the big straplike muscle which runs diagonally across and down the neck to the top of the sternum and the inner end of the clavicle) - take a moment and feel the hard bulge of the mastoid process behind your ear; turn your head to the other side, and feel the sternocleidomastoid muscle running down your neck.
Now place your fingers along the vertical groove in front of your ears, and open and close your mouth - you should be able to feel the movement of the back edge of the mandible - notice that at the hinge at the top, the jaw actually moves very slightly forward on opening - this is because the temporomandibular joint is not a simple ball and socket joint. In fact there are two joint cavities, with a disc of fibrocartilage separating them - the effect of this is to allow the joint to glide forward as well as rotating during opening (the disadvantage is that if the mouth is forced open too far, the joint can be dislocated, and the mouth stuck in the wide-open position!)
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-tmjfunction.jpg
So what are the muscles that close the jaw? - the masseters, temporalis, and medial pterygoids.
The masseters run from the angle of the jaw diagonally upward and forward onto the lower border of the middle region of the zygomatic arch:
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-masstemp1.jpg
Put your fingers on the sides of your face above the angle of the jaw - clench your jaw - feel the masseter muscles contract, and feel along their anterior (front) borders - follow them up to the bone of the zygomatic arch making up the prominance of the cheek - feel along this horizontally forward and back
The temporalis muscle is a large fan-shaped muscle attached in an arc across the side of the cranial bones, which comes together and runs deep to the zygomatic arch, ending on the coronoid process of the mandible.
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-masstemp2.jpg
Put your fingers on either side of your head, and clench your jaw - you will be able to feel the temporalis muscle contract
There are two more muscles attached on the inside of the jaw, the medial and lateral pterygoids
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-pterygoids.jpg
Both are attached to the mandible and to the sphenoid bone. The medial pterygoid pulls the jaw up and forward, the lateral pulls the jaw forward, and the chin down slightly. They may also be used to pull the jaw from side to side
These muscles all cooperate in the process of chewing. The major muscles involved in opening the jaw will be described by me when I discuss the muscles of the tongue and neck.
Here endeth the first lesson :p
Lots more to follow, over the course of the fortnight!
Dave
I'll introduce various topics with additional posts in the course of the 2 week period, (building up information gradually, starting with some basics on the bones), suggest some study exercises, and (hopefully!) answer any questions. I'm particularly keen to point out features which vary with age, sex and ethnicity, as careful attention to these can all help the portraitist achieve a likeness (and give control over the issue of accurate versus flattering!). I'd also like to try to shed a little light on how some of the structural features - for example the structure of the skin and underlying tissues - affect surface appearance. Understanding these factors may help you make someone look younger (or older), fatter or slimmer, for example.
Let's start today with some bony anatomy:
the skull consists of 3 areas
1.the cranial vault, or calvaria enclosing the brain, and
2.the facial skeleton, including the upper jaw (maxilla)
3.the lower jaw (mandible)
These two diagrams show the various bones which make up the skull, colour-coded to make it easier to see how they all fit together.
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-skullfront.jpg http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-skullside.jpg
and here's that side view again, this time with the bones named:
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-skullnames.jpg
Have a look at this pair of casts of skulls - the left hand one is an adult, and the other is a 5 year old - note the difference in relative proportions of the cranial vault versus facial skeleton
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-adultskull.jpg http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-5yrold.jpg
- in the child the facial skeleton is a smaller proportion of the total head, though the orbits are large, as eyes are proportionately larger in children than in adults - and note how there is vertical elongation of the midfacial skeleton in the adult, particularly of the maxilla and zygomatic bones, and of the mandible - this occurs during the teens, and is a factor in the rapidly changing facial appearance during adolescence. Note also the difference between the adult permanent teeth, and the childhood deciduous dentition.
The maxilla is part of the cranium, and the upper teeth are inserted into it - thus their position is rigidly set in relation to the rest of the cranium.
Let's remove the mandible, and look at the skull-base from below:
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-skullbase.jpg
Notice how the majority of the hard palate behind the teeth of the upper jaw is maxilla, and behind this is the palatine bone (here, centrally, in pale pink) - the back edge of that is the attachment of the tissues of the soft palate - above that is the posterior entrance to the nasopharynx.
Note that much of the central skull base area is the sphenoid bone (here in grey), and posterior to it is the occipital bone (in yellow). The large hole in the occipital bone is the foramen magnum through which the spinal cord passes. In humans, the foramen magnum faces inferiorly (i.e. downwards) associated with our upright stance, whereas in most animals the foramen magnum opens posteriorly (backwards). To either side of the foramen magnum, we can see the articular condyles - the surfaces that the first cervical vertebra hinges on. ( We have 7 cervical vertebrae in the neck, between the base of the skull above, and, below, the first thoracic vertebra - which has the first rib attached).
I'd like to turn our attention to the jaw for a while, and its relationships.
Let's look at the hinge area:
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-tmjbones.jpg
If we look at the temporal bone from the side, we can see the auditory meatus - this is where the external ear canal links up to the middle ear - immediately anterior (in front of this) is the temporomandibular joint, between the head of the mandible, and the lower and most posterior part of the zygomatic arch (which in turn forms the bony prominence of the cheek).
Behind the auditory meatus is the mastoid process, where the sternocleidomastoid muscle of the neck attaches (this is the big straplike muscle which runs diagonally across and down the neck to the top of the sternum and the inner end of the clavicle) - take a moment and feel the hard bulge of the mastoid process behind your ear; turn your head to the other side, and feel the sternocleidomastoid muscle running down your neck.
Now place your fingers along the vertical groove in front of your ears, and open and close your mouth - you should be able to feel the movement of the back edge of the mandible - notice that at the hinge at the top, the jaw actually moves very slightly forward on opening - this is because the temporomandibular joint is not a simple ball and socket joint. In fact there are two joint cavities, with a disc of fibrocartilage separating them - the effect of this is to allow the joint to glide forward as well as rotating during opening (the disadvantage is that if the mouth is forced open too far, the joint can be dislocated, and the mouth stuck in the wide-open position!)
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-tmjfunction.jpg
So what are the muscles that close the jaw? - the masseters, temporalis, and medial pterygoids.
The masseters run from the angle of the jaw diagonally upward and forward onto the lower border of the middle region of the zygomatic arch:
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-masstemp1.jpg
Put your fingers on the sides of your face above the angle of the jaw - clench your jaw - feel the masseter muscles contract, and feel along their anterior (front) borders - follow them up to the bone of the zygomatic arch making up the prominance of the cheek - feel along this horizontally forward and back
The temporalis muscle is a large fan-shaped muscle attached in an arc across the side of the cranial bones, which comes together and runs deep to the zygomatic arch, ending on the coronoid process of the mandible.
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-masstemp2.jpg
Put your fingers on either side of your head, and clench your jaw - you will be able to feel the temporalis muscle contract
There are two more muscles attached on the inside of the jaw, the medial and lateral pterygoids
http://www.wetcanvas.com/Community/images/06-Mar-2005/30792-pterygoids.jpg
Both are attached to the mandible and to the sphenoid bone. The medial pterygoid pulls the jaw up and forward, the lateral pulls the jaw forward, and the chin down slightly. They may also be used to pull the jaw from side to side
These muscles all cooperate in the process of chewing. The major muscles involved in opening the jaw will be described by me when I discuss the muscles of the tongue and neck.
Here endeth the first lesson :p
Lots more to follow, over the course of the fortnight!
Dave