Although snakes lack a neck region, as defined in squamates by the positioning of the forelimb girdle, the comparison with Hox gene expression in lizards indicates that a relative normal neck region is patterned.
Interestingly HoxA6 expression coincides with the beginning of the rib-bearing region in both lizards and snake, and our observations do not rule out the possibility that a single Hox gene is responsible for rib formation in these species.
Apparently, though, the mechanism of posterior prevalence, according to which more posterior Hox genes modify these ribs or suppress rib formation completely, is not operational.