When drawing animals, it is very helpful to first note the similarities between human and animals anatomy.
Animals that lie in wait for their prey have large, squat skeletons and powerful legs for springing and short sprints. This group includes lions, tigers, leopards, pumas, panthers, and domestic cats.
We'll begin with a simple diagram to show the general proportions. The length of the head will be used as the unit of measure.
You will draw a diagram as seen below, beginning with the head to establish the unit of measure.
After you draw the head, draw a line from the tip of the nose to the back of the skull. This is your unit of measure. The length of the cat's body, not including the neck and head, is approximately 3 and 1/5 heads long. The height is approximately 2 and 1/2 heads high.
Next, draw a dotted line at the point halfway between the top and bottom of the diagram. This will help you place the joints.
Next, you will add the general shape of the rib cage.
Sketch the profile of a cat around the skeleton.
This diagram is based on an example in The Artist's Guide to Animal Anatomy, by Gottfried Bammes.
Draw another diagram like the one you've just drawn
Using your simplified skeleton sketch for reference, sketch the cat again as a series of simplified shapes, as seen below:
(for more examples of animals sketched in the simplified forms, see Drawing Animals by Norman Adams and Joe Singer)
Below are several anatomical drawings of big cats that will be very useful to copy. The more you copy these, the better you will understand the anatomy and proportions.
For illustrations of skeletons, muscles, and full animals (as seen below) refer to An Atlas of Animal Anatomy for Artists by Ellenberger, Dittrich, and Brown