Alrighty, so there's definitely strong points in your work, as well as a number of areas I want to touch upon - and I'm very pleased to say that I was able to cram all of my notes onto your bison drawing. You'll find them here, but I'm going to go over each point in turn. I've also numbered the notes on the drawing so you can refer to them.

1. All additions should be 3D forms, not arbitrary lines or 2D shapes

This one should sound pretty familiar, because I brought it up in Lesson 4. Everything you add to a construction should be its own complete, enclosed 3D form. You have definitely done this more correctly in other areas (like along the bison's back), but it's clear that you're not quite adhering to that rule as consistently as you should. In the legs, you bridge across from one form to another with a simple line, enclosing a flat shape against the existing forms, but not actually defining how this thing you're adding relates to that existing structure. As a result, it comes off as being flat, and it flattens out the other forms around it.

In the redline notes, I demonstrate with examples involving two ball forms.

2. Make sure your additional 3D masses' silhouettes respond to the actual forms it's touching, rather than just being arbitrary

The easiest thing here is to first thing about the mass as though it exists on its own, in an empty void. Here it'd behave like a soft ball of meat or clay, in its simplest possible state, its silhouette composed only of outward curves. Once you press it up against an existing structure, however, that's when it starts developing more complexity. Parts of the silhouette turn into inward curves, in direct response to the forms it's pressing against. The sides that don't make contact, however, remain simple. Here's a depiction of what I mean.

This essentially means that the silhouette of your additional masses must only be complex where it's touching the structure, and the complexity of that silhouette must directly correspond with those forms. So if you look at my redline drawing, you'll see how the mass has a really bold, obvious inward curve where it wraps around the big shoulder mass. It's got another inward curve along either side, where it's wrapping along the breadth of the torso sausage. These are obvious, and emphasized, because I know precisely the nature of the forms it's interacting with, and in doing so, I'm emphasizing the fact that those forms are 3D.

As a side note - draw through your ellipses, as discussed back in Lesson 1.

3. Use the sausage method when constructing your legs.

You are obviously using the sausage method to varying degrees, but you're pretty inconsistent in how and where you apply its principles. The sausage method isn't pick-and-choose. It's got specific rules, and you've got to apply all of them. Keep your segments to the characteristics of simple sausages, and then define the relationship/intersection between the segments with a contour line at each joint.

4. Head construction

Most of what I want to share here is summarized in this informal demo, so give it a look and be sure to read the written section there as well.

One additional point I'd like to offer is about how you draw the muzzles - the issue here is similar to what I mentioned in point 2, where you're relying more on random blobbiness. Think of the muzzle as a very boxy additional mass. The side that touches the cranial ball is still going to have to form its inward curves to properly "grip" that form, but the outer side is still going to remain boxy in its silhouette. Think about how such a silhouette needs to be shaped in order to give the impression of separate planes. You get those with sharp corners, not with random roundedness.

So, I've outlined 4 major points for you to work on. I'm going to assign a few additional pages below, where you can demonstrate your understanding of these matters.