Some ideas on larger herbivore types. That cervical curve is really going to dip if we make a character with those distinctive rounded shoulders with a neck in a 'stoop'. The nuchal ligaments are going to have to act like a crane arm to help stop that neck collapsing - it's rather unstable. So I've also highlighted some context as to large stabilising muscle shapes of the neck. I think this would really limit head rotation. Also the cervical vertebra in this configuration would have to be bulkier to take the stress of the lateral rotation.

Great video on cervical spine rotation.

Skull to Neck

As heads get bigger, so does the weight of keeping them upright. Here i'm showing the nuchal ligament as being an important part of keeping a larger head upright.

We need to strike a careful balance with how we expect larger anthro skulls to sit on a biped spine. The cervical vertebrae is the most flexible part of the spine but this comes at a trade-off with strength. Strong yet flexible interspinal ligaments hold the vertebrae from palling apart and in many quadrupeds the nuchal ligament is very important in holding the head and neck from collapsing under it's weight. In humans this tough ligament is less important, our skulls are balanced on the 1st cervical vertebrae, the Atlas, with stability aided by numerous muscles. An anthro skull by contrast would likely be heavier, larger facial features, big jaw. This upsets the balance and we can either reposition the skull on the atlas like a pivot or we recruit ligaments and muscles to help stability. Nuchal ligaments would act like a suspension bridge, pulling from the processes on the thoracic vertebrae to a prominent crest on the part of the Occipital bone of the skull.

What does this mean for character designs: 

consider the weight of your characters heads, this includes big horns and teeth! 

How would the cervical vertebrae curve, is it realistic

Where is the load of the head being distributed

Spinal processes are going to be visible along their backs

How will bigger back muscles such as the trapezius look and how is that head able to flex and move?!

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.

Skull Ideas

The muscles of the jaw are rather large on animals both herbivore and carnivore.
This is important for the Zygometic Arch or cheek bone as both the Masseter and Temporal muscles influence its size and shape. Coloured are ideas on visual fields.

I want to make sure a human size brain could fit into something like a horse's skull but make sure that the mouth and nasal pathways were still usable. By enlarging the Occipital or base of the skull can accommodated this. The brow ridge may also help but it means losing the flat Frontal bone that give herbivores their distinctive sloping head shapes. 

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...