Meeting Abstract
Joint articulations determine range of motion (ROM), allowing or restricting particular motions to balance stability and flexibility. Snakes have a unique zygosphene/zygantrum joint in their vertebrae (either minimal or absent in all other vertebrates), but the function of this joint is poorly understood. To experimentally determine the role of the zygosphene/zygantrum articulation in the range of motion in snake vertebrae, two sequential mid-body vertebrae of a cornsnake (Pantherophis guttatus), boa (Boa constrictor), and rattlesnake (Crotalus viridus) were CT-scanned, segmented out, and 3D printed (14x size). Two copies of the posterior vertebrae were printed, one unaltered and one with the zygosphene digitally removed. Motion capture cameras were used to record the angular ROM in yaw (lateral bending), pitch (dorsoventral bending), and roll (axial torsion) as the joint was manually manipulated. Removal of the zygosphene increased yaw ROM but did not affect pitch. In the unaltered vertebrae, roll ROM was minimal for all combinations of pitch and yaw. In the altered vertebra in the cornsnake and boid, roll ROM was unconstrained only when the pre- and post-zygapophyses were no longer articulated (at high yaw angles), a condition that was not possible when the zygosphene was present. In the rattlesnake, roll ROM was minimal for both altered and unaltered vertebrae, as the pre- and post-zygapophyses were unable to disarticulate. Thus, it appears the zygosphene/zygantrum joint acts as a bony limit preventing the vertebrae from reaching high yaw angles where roll could occur, strengthening the joint without sacrificing flexibility.
