Snakes (Serpentes) and lizards (Lacertilia) belong to „scaled reptiles“ (order Squamata) and are the most famous clade of animals in which limb loss occurred. Snake fossils do not have forelimbs while their hindlimbs are well developed. Most recent snakes completely lost their limbs and only clades Booidea and Scolecophidia have rudimentary hindlimbs. The loss of limbs is related to the elongation of the trunk which snakes achieved by accelerating somitogenesis and prolonging the expression of the Oct4 gene, one of the regulators of Hox gene expression. Hox genes are highly conserved regulatory genes responsible for the development of certain parts of the body. Their expression domains are mostly unchanged in snakes, but there are changes in their interpretation resulting in a change in the expression of genes important for limb bud initiation which contributed to limb loss. Also, during embryonic development of limbs in snakes, the establishment of two signaling centers does not occur due to mutations in the enhancers responsible for their maintenance, which ultimately resulted in the complete or partial loss of limbs. In contrast, snakes have preserved some genes that are involved both in development of limbs and external genitalia.