Bracing at the base of the giraffe's neck.

<p>The base of the giraffe's neck is braced to protect the intervertebral joints from excessive strain on their synovial capsules and to rigidify the neck as it reaches the limits of range of motion. As the neck is raised at the base (A), the postzygapophyses of C7 travel posteriorly until they wedge into depressions in the neural spines of T1 just behind the prezygapophyses (see arrow). Another bracing scheme applies when the neck is deflected laterally (B), In defecting the neck to the left, for example, C7 bears against the left postzygapophysis of T1, see arrow. In either dorsal or lateral flexion the two vertebrae progressively lock up firmly and stably. At these extremes the zygapophyses maintain substantial overlap (roughly a ZSF of roughly 0.5). CT data provided courtesy American Museum of Natural History and Timothy Rowe, University of Texas. Supplemental material: <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078572#pone.0078572.s005" target="_blank">Movie S2</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078572#pone.0078572.s006" target="_blank">Movie S3</a>.