Several other less distinct breeds might be specified.
In the skeletons of the several breeds, the development of the bones of the face, in length and breadth and curvature, differs enormously.

The shape, as well as the breadth and length of the ramus of the lower jaw, varies in a highly remarkable manner.

The caudal and sacral vertebrae vary in number; as does the number of the ribs, together with their relative breadth and the presence of processes.

The size and shape of the apertures in the sternum are highly variable; so is the degree of divergence and relative size of the two arms of the furcula.

The proportional width of the gape of mouth, the proportional length of the eyelids, of the orifice of the nostrils, of the tongue (not always in strict correlation with the length of beak), the size of the crop and of the upper part of the oesophagus; the development and abortion of the oil-gland; the number of the primary wing and caudal feathers; the relative length of the wing and tail to each other and to the body; the relative length of the leg and foot; the number of scutellae on the toes, the development of skin between the toes, are all points of structure which are variable.