Cockerell states that he finds Chapman's zebra a very good species to use for the process of measuring skulls. He details at length the various measurements of skulls from the different Equus species, and encloses remarks made by James W. Gidley on this subject.

Cockerell states that he wishes he could conduct experiments on horses in New Mexico as the conditions are very favourable. He mentions that Wilfred Blunt is also of the opinion that the native American horse may have lived to Columbian times. At present he is looking for mixed blood in the skulls of American horses. He points out that the old horses of Europe also had large heads. He also adds that he has found a copy of an aboriginal pictograph representing a man on a horse.