Final answer:
The specific muscle that is found in cats but not in humans, located in the posterior compartment of the forearm, is not provided in the data. Humans have muscles like the abductor pollicis longus and extensor digitorum in this area, but the unique cat muscle is unspecified.
Step-by-step explanation:
The muscle in question that is found in the posterior compartment of the forearm of cats but not in humans is not specified in the provided information. In humans, the deep posterior compartment of the forearm includes muscles such as the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis, as well as their associated blood vessels and nerves. The superficial posterior compartment of the forearm includes muscles like the extensor radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris. These muscles are responsible for extension and abduction of the wrist and fingers. However, there might be anatomical differences between species, including the presence of additional muscles in cats that humans do not possess.