Activity of three muscles associated with the uncinate processes of the giant Canada goose Branta canadensis maximus.

The activity of three muscles associated with the uncinate processes, (i) external intercostal, (ii) appendicocostalis and (iii) external oblique, were examined using patch and sew-through electrodes during sitting, standing and moderate speed treadmill running in the giant Canada goose. The external intercostal muscles demonstrated no respiratory activity, being active only during running, suggesting they play some role in trunk stabilisation. The appendicocostalis and external oblique muscles are respiratory muscles, being active during inspiration and expiration, respectively. The activity of the appendicocostalis muscles increased during sitting, suggesting that the uncinate processes in birds play an important role in facilitating lateral flaring of the rib cage when sternal rocking is prevented. We suggest that the uncinate processes in birds facilitate movements of the ribs and sternum during breathing and therefore are integral to the breathing mechanics of birds.