The muscles have been reflected to make it easier to see how they overlap. The arrows are pointing toward the insertion of the xiphihumeralis (1), pectoralis minor (2), and latissimus dorsi (5). Study this picture carefully and then return to your cat and make sure you understand how these muscles are related.

In this view it is also possible to see how the pectoantibrachialis (4) inserts on the fascia of the lower arm.

Thoracic Muscles
Looking into the arm pit