I've updated this with a newer version here: [link]

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This certainly took long. Oh the endless labeling...
I'm not entirely happy with the look of the muscled body, so I may update it later.
Much thanks to the Cyclopedia Anatomicae and the Manual of Ornithology, as well as to and all of which I referenced heavily.

This is a large file, so full view to read the labels. This come with a warning, I am not an expert on anatomy or the complications of flight. (For example, I'm still not convinced if those small bones lining and stiffening the tail are called chevron). This is my attempt to create an anatomy reference for myself based on my current understanding of a plausibly realistic dragon. On that same note, this is not a reptilian dragon. I always describe my dragons as homeothermic. To clarify: dragons would be in their own group altogether separate from both mammals and reptiles, due to their extra limb set and other extreme differences.
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Anyway, to the basics: This is a fairly boring design, and is meant to serve as a base with which to form wilder and more exaggerated creatures. This example is based equal parts on a lion, eagle, pterosaur and velociraptor. I took creative liberties with some of the anatomy to serve my own purposes, unlike in birds, the dragons back is not made up entirely of the fused thoracic vertebrae as he still has some lumbar vertebrae in the back for flexibility. I want the dragon to be able to run effectively and hunt both aerially and terrestrially. I also left out any kind of stabilizing device fan or tail feathers to keep the dragon extremely rudimentary in design.

The dragons head is based on both a lions and a dromeosaurs, I gave him more of a jaw than a raptors for added bite power. He also has some optional facial musculature for the purposes of expression. If I wanted to be extremely realistic, he would have neither teeth nor the bulkier jaw because of the excess weight, but what fun is a toothless dragon?

Some of this may be quoting John Conway's pterosaur research: The Pulmonary SASS (Subcutaneous air sac system) are a complex system of air sacs located beneath the skin that act as bellows for the lungs as well as to pneumatisize bones -filling them with air, meaning the bones can be bigger without being heavier or weaker. To be specific, they have post-cranial skeletal and soft-tissue pneumaticity; meaning there are hexagonal (honeycomb structured) spaces and pneumatic foramina filled with air within the bone and some tissue. The pneumatisation in the wings perhaps being fueled by the SASS. The air sacs may have have played a structural role in holding wing shape and posture, as they do in some birds. This feature aids in the oxygenation of the muscles, and unidirectional flow of oxygen in the lungs. Their large lungs, coupled with their efficiency of exacting oxygen from the air serve to support their size and powerful flight muscles. The SASS would also allow the animal to control the mechanical properties of the wing, perhaps even allowing the inflation to be used in display as it does in some birds.
Also from pterosaurs- the top layer of the wing is the actinofibrils, which help give shape and support to the wing.

About necks ((Knut Schmidt-Nielsen's “How animals work”, page 49 (1972))-
Long necks developed in dragons as well as in some birds and pterosaurs to allow ease of breath. Most dragons had long to mid-length wings for efficient flight and powerful downward thrust, but low wing beat frequency. And as wing-beat frequency determines respiratory frequency, this calls for bigger longer breaths, so a longer trachea and therefore longer neck is required to breath deeply without hyperventilating in flight. This creates the right dead space to tidal volume proportion to create the correct mixture of dead space air and fresh air upon inhalation and co2 concentration. Smaller dragons with shorter wings, higher wing beat frequency and shorter breath do not require this, and so have shorter necks.

Teeth- the dragon possesses incisors and canines similar to a lion and carnassials/molars for sheering and crushing. The other teeth (don't know the technical term) have strongly serrated backs and curve backwards like a raptors for holding onto prey.
The crushing back molars are useful for chewing bone as well as the minerals needed to spark their hydrogen and breathe fire. The hydrogen is produced by the dragons corrosive gut as a digestive byproduct and is stored in two long lung-like bladders that keep the dragon lightweight.




EDIT: Oh wow, a DD? Thanks guys so much!