From the outer tuberculum extends the large crista superior (insertion of pectoralis major and of deltoideus major muscles).
The ventral portion of the neck is formed by the strong crista inferior, on the median side of which is the deep fosses subtrochanterica by which air sacs enter the humerus.
On the outer side of the humerus between the head and the crista inferior is a groove lodging one of the coraco-humeral ligaments.
The most novel feature, and one the importance of which most ornithologists of the present day are fully prepared to admit, is the separation of the class A y es into two great divisions, which from one of the most obvious distinctions they present were called by its author Carinatae' and Ratitae, 2 according as the sternum possesses a keel (crista in the phraseology of many anatomists) or not.
The middle valley is often intersected by vertical "crista" and "crochet" plates projecting into it from the anterior surface of the posterior transverse ridge or from the wall, the development of which is a useful guide in discriminating species, especially those known only by teeth and bones.