Vampires are descended from mortals. They're dead mortals kept alive by the curse. Accordingly, the anatomy of the undead is only slightly different from that which they already had in their mortal lives.
Although most vampires are descended from humans or elves, there are also some dwarven or even orcish vampires, who, however, are no better off in vampire society than they were in mortal society.
Differences from mortal anatomy
Although the anatomy of the species remains largely unchanged, death does not leave anyone untouched. In the course of the transformation, new muscles are formed in the upper jaw, which allows the muzzle to retract, so that they are not permanently visible. These muscles are activated voluntarily when drinking or involuntarily when hungry, scared or in combat situations, which is why the vampire's fangs become visible in such situations.
In the first few days after the death of the body, the change that makes the vampire so desirable to mortals sets in. The body fat percentage drops massively, any excess pounds disappear and leave the vampire slim, even almost lean. For this reason, many male vampires appear either very lanky or very muscular concerning their physique.
The internal organs wither away within the first weeks after the death of the mortal body, leaving only dried, completely useless tissue behind. The vampire's entire metabolism is now geared to blood, which he or she urgently needs for survival. The need to breathe evaporates at the very moment of death.
However, every vampire can give himself a glimmer of life by making his dead heart beating and pumping blood through his veins again. This action is quite exhausting and increases the vampire's need for feeding.
The undead develop a massive allergy to sunlight, which causes spontaneous combustion. This allergy is much more pronounced in older and more powerful vampires than in young or weak vampires, who can hardly be counted as undead.