The trachea or windpipe is strengthened by numerous cartilaginous, often osseous, complete rings, but in the emeu several of these rings are incomplete in the medioventral line, and permit the inner lining of the trachea to bulge out into a large neck-pouch, which is used by both sexes as a resounding bag.
The skeleton is cartilaginous, and the skull is remarkable for the very elongate suspensorium of the lower jaw; the tail remains in the notochordal condition, no cartilages being formed in this organ, which is destined to disappear with the gills.
The intervertebral joints are further complicated by the interposition of a cartilaginous or fibrous pad or ring.
The keel, or carina sterni, is formed as a direct cartilaginous outgrowth of the body of the sternum, ossifying from a special centre.
It is absent in the Ratitae, which from this feature have received their name, but considerable traces of a cartilaginous keel occur in the embryo of the ostrich, showing undeniably that the absence of a keel in the recent bird is not a primitive, fundamental feature.
