Final answer:
In adult limbs, the pre-axial border is found on the thumb side of the upper limb and big toe side of the lower limb, while the post-axial border is on the little finger side of the upper limb and little toe side of the lower limb. The appendicular skeleton is formed from hyaline cartilage models during embryonic development, wherein limb rotation establishes the final limb orientation.
Step-by-step explanation:
The structures we use to identify the pre-axial and post-axial borders in adult limbs are associated with the developmental process of the limbs during embryogenesis. During the sixth week of embryonic development, the limb buds form, eventually differentiating into the upper and lower limbs. The pre-axial border of the limb corresponds to the radial (thumb) side of the upper limb and the tibial (big toe) side of the lower limb. Conversely, the post-axial border corresponds to the ulnar (little finger) side of the upper limb and the fibular (little toe) side of the lower limb.
The skeleton of the appendicular system includes the upper limbs (arm, forearm, wrist, hand) and lower limbs (thigh, leg, ankle, foot), differentiated by the respective girdles - the pectoral for the upper limbs and the pelvic for the lower limbs. The pelvic girdle significantly differs between adult males and females, with features suited for childbirth in females, such as a wider subpubic angle, a more circular pelvic inlet, and broader hips.
The process of limb development additionally involves the formation of hyaline cartilage models which act as the precursor to bone formation in the limbs. This process includes the rotation of limbs, where the upper limbs rotate laterally and the lower limbs medially, setting the final orientation of the limbs as seen in adults.