FORM AND FUNCTION

A picture is worth a thousand words in explaining the bone structure that underlies the ability to freely turn the head, which is found not only in Saddlebreds but in some Thoroughbreds, Arabians and warmbloods. In skull A, the plate of bone that forms the occiput is tilted backwards relative to the top of the braincase, producing an angle (marked in red) of well over 90 degrees. This displaces the joint between the skull and the atlas vertebra rearward, which in turn widens the distance between the “wing” of the atlas and the back of the mandible (the jowl). Skull B is typical of most Thoroughbreds or Quarter Horses, having less backward tilt of the occiput and thus a shorter distance between the wing of the atlas and the jowl. The bones colored red, blue and green are the squamous temporal, mastoid and paramastoid bones, which overlap in Chinese-fan fashion and are spread farther apart in horses with back-tilted occiputs.

Space between the wing of the atlas and the jowl has often been cited as making it easier for a horse to carry its head vertical when ridden. What is usually forgotten is that this also increases the range through which the horse can swivel its head sideways on the end of its neck. The joint between skull and atlas is formed between the occipital condyles of the skull (abbreviated OC), which are shaped like a pair of kidney bean-shaped knobs, and the forward aspect of the atlas, which has matching cups into which the occipital condyles fit. Up-and-down “yes” movement of the head is facilitated at this joint, but the condyles can also slide sideways in the cups, permitting the Saddlebred horse to turn its head up to 90 degrees without curving its neck.