The snake lateral plate mesoderm shows a collinear pattern of Hox expression as has been implicated in the positioning of the limbs in chicken.
No limb buds are present in corn snakes however, and neither is any molecular trace of a discrete forelimb domain.
In contrast to the potential upstream regionalizing signal provided by differential Hox expression (especially HoxB9), the expression of Tbx5 is highly deregionalized, being expressed throughout the AP extent of the axis.
Although the observed misregulation of Tbx5 on itself does not explain the absence of limb(bud)s, this suggests that in the snake an uncoupling has occurred between the Hox expression in the lateral plate mesoderm and the normal downstream, limb field inducing gene program.