Anthro leg structure 3

Following from the previous post... now that I know to turn Google image enhance off so that it stops turning all my images black...

Unguligrade legs on the left and digitigrade on the right.

Another way to think about the tapering limb as it becomes more distal is to think about 'muscular bulk', 'taper' and 'tendon'. We have the main muscle bulk at the origin of the limb, the muscle tapers down towards the tendon and finally terminates as just tendon onto the bone. This can be applied to any individual muscle of a limb (fig. 2) or also to the limb as a whole (fig. 1). Drawing a limb with this in mind ensures it stays in proportion.

The proportions of the limb are indicated by the measuring arrows. The set of legs on the left have a shorter thigh in proportion to the more distal, (further from the body) part of the limb; this limb configuration would offer the character the ability to run faster. As I touched on this in a previous post, a longer distal portion of the limb offers a greater stride distance and holds more elastic strain energy, quickening the limbs movement. The legs of the digitigrade on the right have a proportion of thigh to lower leg almost 1:1, similar to us as plantigrades. This would offer more limb stability rather than speed with the joints being less prone to stresses or twisting.

One thing to note is that the stability and speed configurations can apply to both digitigrades and unguligrades; it would simply be species and character dependent.

Head shapes 2

The point of looking over skulls in the first place is to gain some idea of the forms that they lend to the shape of the head and face. One aspect of creature design a friend pointed out was using these observations to help make choices in accessory design. Again, somewhat dependent on the class of species and actually if you work the problem through you end up with some plausible if not odd looking results..

Any eye wear is going to need a much wider bridge. Glasses don't have to be designed to hook round the ears but if they did the arms would need to sit higher and not to the sides like for a human.

Head shapes

I better post some of the sketches I've been sitting on! I've been thinking about skull shapes for anthros for sometime. Previously I looked at the need for anthro skulls to have a cranial dimension like that of a human, if you're thinking intelligence it seems fitting to exaggerate an animals skull to hold a similar brain size to a humans.

The 2 small intermediate diagrams show the distinction of cranial size (red), 
nose/face area (blue) and jaw (green).

Animal skulls are much more elongated front to back than a human's. Where you'd draw an average human skull as a sphere with a box below for the jaw, for an anthro you're looking more at a ovoid with a box at the front. This is so you can retain the distinct facial features such as those elongated noses and jaws. You can break this idea down further into class (I take class to mean either carnivore, omnivore or herbivore). The main distinction between them being the required jaw size to tackle their specialised foods. As a general idea, jaws tend to get both longer and deeper with herbivores; more muscular action is needed to grind plant matter, so a large bone surface is required, their food is generally in a hard to reach place, hence the long face. For either class, starting with a skull similar to that of a human guarantees you'll retain an adequate brain size.

Taking this a little further the idea of snout length is certainly up to not only the species and the class but also to your own preference. Felines tend to have a much rounder short snout, canines have a more rectangular and thin snout. Length adaptation is up to you. For example, the sketches above are for carnivores, their main principle is that their jaws are thin and sleek with large forward pointing eyes however the length of the snout is undefined.

Jaws are nothing without teeth, and teeth are distinctly specialised for each class. There are a number of other more subtle differences than teeth to think about, especially if you want to be creating expressive characters. Jaw depth i've mentioned, however it's carnivores that tend to have a much larger jaw opening range to catch and eat pray. Useful for expressions showing rage and anger. Due to their large teeth, particularly their canines, carnivores have limited side to side motion which herbivore use to rotate their jaws to grind plant matter. Side to side motions are more or less reserved to show puzzlement or thinking. 

Ahhhhhh a splinter!

Huh?

Lumbar Support

I've gone back to thinking more about spinal curves when it comes to anthros. This is particularly relevant with tough, heavy types and also very relevant when thinking about how a tail would be structured and function on a biped. I think that the fundamental understanding of what can and can't be done with anthros bipeds certainly concerns the lumbar support system.

Part of the lumbar lordosis support

The human S-curve transfers tension and load down into the pelvis via the sacro-iliac joint. If we are going to retain anthro features such as larger skulls, bigger chest and shoulder like that of Minotaurs, the more weight we are applying to the cervical and thoracic vertebrae, ultimately pulling the torso forward as well as the centre of gravity. This is going to make it harder for this S-curve to hold it's mid-line (shown in red). If the mid-line shifts away from the sacro-iliac joint then weight transmission is less efficient, resulting in muscle groups having to bear the torso's load rather than the spine. 


In humans an important deep structure called the thoracolumbar fascia, which are tough multi-directional connective tissues directly attached to the spinous processes of the lumbar vertebrae. Our erector spinae muscles and latissimus dorsi, as well as our core muscles such as the obliques act to pull the thoracic spine (our chest) backwards and downwards, keeping us held upright. The gluteals as I've mentioned in previous posts are under tone to hold the pelvis from tilting forward, keeping us stood upright. These multiple actions ultimately draw the lumbar spine into lordosis like drawing the string on a bow, the lumbar curve is under a great deal of elastic energy, stored in the thoracolumbar fascia.


Understanding the limits of the lumbar curve is important for anthro characters, who are often portrayed as extra massive, with craning necks and heads. The spinal curves may have to adjust to hold this weight and maintain the mid-line, either through hyperlordosis or even kyphosis.

How the sacro-iliac joint and the lumbar curve would be arranged to structure a tail is a relevant question. It would certainly require changes to the configuration of the pelvis as well as considerations on nerve pathways out of the sacrum.

More on the thoracolumbar fascia:

Stance sketches

Some ideas on digitigrade and ungiligrade legs this week. I'm hoping to have the time this month to complete some 2D animations on walking.

Way is knowing the pelvic structure important?

It’s a good idea to note the configuration of the pelvis when creating any character, human or anthro. I'm a firm believer in sketching out the basic bone structure in any character sketch, it helps to create your anchor points and maintain your proportions. There are a number of landmarks of the hip that will dictate the overall look of your characters waist, hips and legs that are worth taking some time to study.

Landmarks from the front:
1. The iliac crest, the most obvious part of the pelvis you can feel under the skin. In an athletic character the crest forms the ridge to the bulging mass of the obliques, the muscles of your waist.
2. The inguinal ligament is formed by the obliques and demarcates the line where the torso ends and legs begin. It creates the distinctive 'V' or 'U' shape seen in the photo below.
3. Pubic tubercle this forward projection of the pubic bone can be felt under the public line and is the attachment of the inguinal ligament. The abdominal muscles also attach to the pubic bone. Below this landmark is the point at which the genitals sit, in the male for example via the suspensory ligament. (Also worth noting is that if your characters are in 'heroic' proportion, that's 8-heads high, this landmark marks the mid point of your character height).
4. The greater trochanter of the femur is the major attachment point of the gluteals. It is clearly visible in a frontal view as a bulge at the top of the leg and more predominant in the female. It adds a distinctive curve to the top of the leg when drawing characters from the front or back.

The distinctive 'V' or 'U' shape of the obliques.

Standing upright - Part III

In Part I I looked at changes in pelvic configuration from early hominids. It’s useful to note these changes as it helps explain why we are good at being bipedal and conversely, what wouldn't work or work very well. I’ve laid out what I’ve found here in terms of adaptations to the pelvis from quadruped to biped, these can act as our ‘ground rules’ for consideration when designing anthro characters or mechanical walkers.

Points to consider:

• Centre of gravity – bipeds must make sure their centre of gravity doesn't shift drastically from side to side with each step, this is destablising and inefficient.
• A tall pelvis has the effect of lengthening the torso, meaning that the centre of gravity moves higher, further away from the hips. This makes the trunk harder to stabilise.
• The ‘S’ curve of the lumbar vertebra lowers the centre of gravity towards the hips, helping stabilise the torso.
• This lumbar curve also gives the vertebral column the flex needed to withstand the pressure of the torso acting through it, the lower lumbar have widened giving a larger surface area for weight transmission.
• A wider sacrum has evolved to accommodate the wider lower lumbar vertebra. The sacroiliac joint (connecting the sacrum and the pelvis) also has a large surface area for weight transmission from the torso through both sides of the pelvis down to the femoral heads.
• The widened sacrum increases the width of the 'true pelvis', (the space through the centre of the pelvis), facilitating the ability to birth offspring with much larger craniums.
• However, a wider pelvis is a problem. During the support phase of locomotion one leg is off the ground. The weight of the torso is now acting on the femoral head of the standing leg. This is an example of a first class lever (levers that balance weight like a child's see-saw). The femoral head is acting as the pivot and the distance from the pivot to the body weight is called the 'load arm'. The ‘force arm’ on the other side of the pivot is our gluteus medius (an abductor muscle). It contracts to counterbalance the load arm. The wider we make our pelvis the longer we make the load arm, putting more pressure on the femoral head. We need a larger force or longer force arm to increase the mechanical advantage of this lever, otherwise we risk damaging the femoral head or having the hips slump with each step, just like the chimpanzee. In the Lucy skeleton, Australopithecus afarensis, it reveals her long load arm was countered by an increased length in the neck of the femur and a flaring of the iliac crest of the pelvis to place the abductors further from the pivot.
• The bicondylar angle is unique in humans. The femurs converge at the knees, bringing the legs close to the midline. This means the feet pass close to the midline and the centre of gravity is maintained directly underneath the torso. This is energy efficient as it doesn’t create a side to side motion of the hips when we walk.

Standing upright - Part II

It isn’t possible to directly compare a set of quadruped ‘buttocks’ to that of a human because for quadrupeds, like the horse in this example, their behinds are not really gluteals, they are hamstrings. I'll bang on about these muscles groups just once more:

Hamstrings: in quadrupeds serve as powerful hip extensors, driving the animal forwards against the ground reaction and pulling the leg up and backwards to take the next stride, whereas in humans their action is similar but less powerful due to them being almost vertical when stood upright. Importantly, in bipeds they counteract the truck from falling forward.

Gluteals: in a quadruped, are powerful locomotors also extending the hip, in humans these would relate to gluteus minimus and medius and are now adapted to stabilise the hip laterally, most notably when we stand with one leg off the ground, rather than being used for locomotion. In bipeds the gluteus maximus takes more of the role of hip extensor via the ilio-tibial band. Gluteus maximus also counteracts the truck from falling forward.

Take a look at the action of the race horses legs, you can see all that ground force coming from the contraction of the hamstrings at the back and gluteals at the top of the hind limb pulling them backwards and driving the horse forwards. 

The gluteus maximus dominates in humans, its function still makes it a powerful hip extensor but it’s role in stabilising, holding the femur and pelvis in alignment, keeps us stood upright. This makes it a very important muscle for bipeds. (Also worth noting that a large gluteal makes it easier for us to sit down).

Dependent on your furry character’s needs, be them straight legged or bent kneed, their gluteals and hamstrings are going to function slightly differently, be sized accordingly and maybe even positioned differently. All that is going to be aided by the configuration of their pelvis.

Expression

Some main human facial movements compared with those need for an anthro' character with a longer muzzle.

Some ideas on the muscular arrangement needed on an anthro' characters face to fulfil human expression and speech. Note that the zygomatic bone is one of the most important areas of the face, anchoring the large masseter of the jaw (for this herbivore) and the zygomaticus and levator labii muscles to control lift of the mouth for smiling. Ultimately the shorter the muzzle the finer these small expressive movements can be, he'll probably still end up curling his lips! I'd need to spend time on how this would look if fur where to cover the face.

Comparative Skull Proportions

Each skull is divided simply into 3 parts; red - the maxilla and the plains of the 'face'; green - the mandible; blue - the cranial vault; yellow - the Axis (1st cervical vertebra). Each represents to a rough scale the respective size of each skull element in a) human, b) canine and c) equine. Note the cranial vault does not directly represent respective brain size.

I've started with a thought on the sentient issues of anthro' characters. We would expect our characters to the be the singing, dancing types of the average human. So if we take the casual assumption that to have the same level of intelligence means having the same brain size of a human we soon need to adjust the proportions of the skull to accommodate this. Fig 2 indicates  a size of the cranial vault in blue of a human (a) that we'd need to apply to our animal skulls. How then do we balance this with the large jaw and jaw muscles of a herbivore or carnivore? What changes does a larger cranium make to that of the facial plains, particularly the Zygomatric (or cheek bones), the position of the eyes and visual field? We have a number of considerations to make and plenty of permutations dependent on species...

S-spine, C-spine

Comparison of axial skeletons of a human and canine, arrows note the number and directions of each spinal curve. (Not to scale).

We encounter an extreme number of issues when converting quadruped anatomy to that of a biped. Essentially it boils down to the evolution of each systems handling of its centre of mass. Human bipeds balance their weight over 2 legs, with the centre of mass moving between each stance leg, however a quadruped dog shifts its weight between fore and hind limbs during movement.

The spines of each system are therefore adapted to cope with each of these extremes. The S-shape spine of a biped has 4 notable curves, creating it's distinctive S shape. This maintains the centre of gravity when standing from the top of the spine down through the feet. These curves also facilitate weight transference with minimal effort. 

The C-shape spine of quadrupeds have only 3 notable curves that are near opposite to biped curves. The C-shape comes from the thoracic and lumbar regions curving upwards. I've drawn the canine above stood upright, this would bring it's centre of gravity in front of its feet, causing it to be unbalanced and fall forward. The curvature of its spine, particularly at the lumbar region would not support the weight of an upright torso, the curve is in the wrong direction.

This shows that we simply can't start our anthropomorphic characters by just standing a quadruped up on 2 feet. This and other anatomical issues make this a poor starting point, however, should we wish to maintain a degree of our chosen animals features in our anthropomorphic bipeds we can start adapting this anatomy into likely possibles. Lets explore these possibilities...