Figure 10. Osteological stops.

The posterior cervicals of camel Camelus dromedarius (A) show pronounced depressions (see arrow) where the postzygapophyses make contact just posterior to the associated prezygapophyses with which they articulate. At the limit of travel in dorsiflexion the zygapophyses remain in overlap (contra [80]) and compression forces can be transmitted through the zygapophyses as the neck becomes effectively rigid and stable at the extremes of dorsiflexion. Pronounced osteological stops are also exhibited in many birds, such as the Greater Rhea Rhea americana (B, see arrows). Photographs by the author; rhea specimen at the Zoology Museum, University of Cambridge, access courtesy Matthew Lowe, and the camel vertebrae are at the Condon Museum, University of Oregon.