Posterior compartment of the forearm Posterior compartment of the forearm The posterior compartment of the forearm (or extensor compartment) contains twelve muscles which are chiefly responsible for extension of the wrist and digits, and supination of the forearm. It is separated from the anterior compartment by the interosseous membrane between the radius and ulna. There are generally twelve muscles in the posterior compartment of the forearm, which can be further divided into a superficial, intermediate, and deep layer. Most of the muscles in the superficial and the intermediate layers share a common origin which is the outer part of the elbow, the lateral epicondyle of
Extra-pair copulation have longer tails. A similar pattern has been found for black-capped chickadees, in which all extra-pair males had higher rank than the within-pair males. But some argue that genetic benefits for offspring is not the reason females participate in EPC. A meta-analysis of genetic benefits of EPC in 55 bird species found that extra-pair offspring were not more likely to survive than within-pair offspring. Also, extra-pair males did not show significantly better ‘good-genes’ traits than within-pair males, except for being slightly larger overall. Another potential explanation for the occurrence of EPC in organisms where females solicit EPC is that the