This dog has the noble but soft expression we expect to see in the Tibetan Apso.  The foreface projects from the skull parallel to the horizontal plane of the skull.  The jaws are level, suggesting strength, but no projecting lower jaw or "chin" is seen.  This dog is a 6 year old male, bred in the USA, he has a reverse scissor bite, and his muzzle is exactly 1/3 of the total head length.  His head width, at its widest point (bizygomatic) is equal to the length of his skull, and is exactly 2/3 of the total length of the head.

This classic bitch demonstrates the straight foreface, and correct length of muzzle.  Her almond shaped eyes are neither too large and round nor too small and close set.  Her large prominent nose leather is correct.  In this photo, she appears to be lacking in underjaw, and one might speculate that her bite would be overshot.  Often, the underjaw will not appear prominent when the nose leather is of good size which it needs to be for high altitude respiration. This bitch has a good sized nose leather with a correct reverse scissor bite.

Here are some examples of correct and incorrect head type in a "cut down" Apso.