Horse outward similarity is an unreliable measure of relatedness. Besides the horse, there are six other species of genus "Equus" in the Equidae family. These are the ass or donkey, "Equus asinus"; the mountain zebra, "Equus zebra"; plains zebra, "Equus quagga"; Grévy's zebra, "Equus grevyi"; the kiang, "Equus kiang"; and the onager, "Equus hemionus". Horses can crossbreed with other members of their genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey). Other hybrids include the zorse,
Equus (comics) foot long (with those corresponding to his thumbs considerably smaller), and while their composition is unknown, they are capable, given the physical strength Equus is capable of exerting with them, of piercing Superman's skin. Equus, the third version of the One Man Army Corps project, along with his predecessor, the second version, had their amygdalae enlarged as part of their genetic modifications, though this was scaled back for the subsequent versions, according to Mr. Orr, because this made the subjects psychotic. Specimens from the project that produced Equus were also said to have the wingbones of a fallen angel within