Anatomical differences in three wing muscles of the Grey heron (Ardea cinerea), the Common buzzard (Buteo buteo) and the Common kestrel (Falco tinnunculus): a possible functional interpretation

Abstract

In this paper, a description of the coracobrachialis caudalis, the scapulotriceps and the extensor carpi radialis muscles is presented in three different species (Common kestrel, Common buzzard and Grey heron) that exhibit notably differing flight styles. The primary goal of this research is to describe the gross anatomy of species not previously examined. Secondly, we attempt to advance a functional interpretation of the structures studied, to understand if such noticeable differences in flight style could have induced a differentiation in the above mentioned wing muscles. Regarding the coracobrachialis caudalis muscle, the Grey heron exhibited an unusual conformation with two “reversed” heads and a great amount of fibrous bundles. Moreover, the “anchors” of the scapulotriceps muscle were well developed in the Grey heron and vestigial in the Common kestrel, while an intermediate situation was observed in the Common buzzard. In addition, the extensor carpi radialis muscle showed interesting findings concerning the number of heads and their disposition. Our data may corroborate some previously advanced functional interpretation. In particular, the structure of the coracobrachialis muscle is in line with the hypothesis of its role as muscular strut. Moreover, the humeral and scapular anchors could play a role in increasing the scapulotriceps tension during some phases of the beat cycle or it may be involved in maintaining wing posture. Regarding the different number of heads and the disposition of the extensor carpi radialis muscle, we believe that it could play a role in maintaining the wing position. Although a correct functional interpretation can be obtained only through multidisciplinary studies, we believe that an in-depth gross anatomy study should always be conducted beforehand, to serve as basis for further and more specific research.