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The anatomy here, in general, isn't bad. There are some issues with the neck, but I think you have a good grasp of the human body.

However, the proportions in this is off in many places. For one thing, his head is way too small for his body. If this guy is supposed to be a lean-muscular type, he should have no more than 3-heads width for the shoulders, but this is more like 3 1/2-4 heads wide. Typical anime characters tend to lean more towards 2 1/2 heads-3 heads shoulder wide, for future reference.

His ear is HUGE and at the wrong angle. The length of the ear is okay (maybe a little too big), but it's way too wide. The width should be 1/2 the length, at the very least. It differs from person to person, but in a 3/4 view the ear shouldn't that frontal. You might see that kind of ear on a profile view, but definitely not a 3/4.

The neck doesn't work very well because once again, the head is too small. If you made the head bigger, obviously he'll need a wider neck, which should fix the strange look the neck has. However, if I may add, a guy's neck tends to be more blocky than a gently sweeping curve. Make the shoulders more prominent to emphasize his masculinity, and make the connection between the neck and the upper chest less diagonal.

His left arm (viewer's sight: right) is good, but the right arm is messed up. For the arm to emerge behind his back like that, less of the upper arm should be showing.

There's a bit more I want to comment on, but I am not as familiar with certain anatomical structures. But, be careful with the hips and the legs. Even if you were just going with a half-view, you should still consider the legs as part of this character, not something to be drawn in last minute.

Hope it all helps.