The Appendicular skeleton is one of the divisions of the endo skeleton. It includes the pectoral and pelvic girdles and limb bones. The skeleton of the limb in all the tetrapods shows a similar fundamental and structural similarity. However the differences such as arms, legs, wings and paddles are seen in the respective animals. A few tetrapods have completely lost one or both pairs of appendages. The limbs are totally absent in caecilians, most snakes and snake-like lizards.The Appendicular skeleton is one of the divisions of the endo skeleton. It includes the pectoral and pelvic girdles and limb bones. The skeleton of the limb in all the tetrapods shows a similar fundamental and structural similarity. However the differences such as arms, legs, wings and paddles are seen in the respective animals. A few tetrapods have completely lost one or both pairs of appendages. The limbs are totally absent in caecilians, most snakes and snake-like lizards.

The typical tetrapod hind limb can be divided into three seg­ments. The thigh, shank and foot (pes) are the three segments. If there are five toes, normally this type of limb is known as pent dactyl limb.

 

The skeletal structures of the hind-limb consists of femur, tibia, fibula, tarsals, metatarsals and phalanges.

The femur is the bone of the high and its head articulates with the acetabulum. Its distal end articulates with fibula. The tibia and fibula are the bones of the shank region. They articulate with femur proximally and distally with the tarsal’s of the ankle bones. The fibula bears the most of the body weight.

The foot can be divided into ankle, instep and toes. The ankle is supported by tarsals, which are arranged in rows. The skeleton of ankle or tarsus is the most stable of the regions of the ankle. The instep or metatarsus is supported by the metatarsals. These are elongated bones. The metatar­sals are followed by linear series of phalanges of the toes. The phalanges number varies from 1 to 5.

The first toe of the hind limb is called 'hallux or great toe' and the fifth toe is the 'minimus'.

 

Calotes (Garden Lizard)	Columba (Pigeon)	Oryctolagus (Rabbit)
1. The bones of the hind limb are femur, Tibia, fibula, tarsals, metatarsals and phalanges.	1. The bones of the hind limb are femur, tibia, fibula, tibiotarsus, tarsometatarsals and phalanges.	1. The bones of the hind limb are femur, tibia fibula tarsals, meta tarsals and phalanges.
2. The femur is stout bone of the thigh region. It has long, slender and curved shaft in the middle. The shaft enlarges at both the ends.	2. The femur is a stout bone of the thigh region. It has a long, curved shaft in the middle. The shaft has broad ends.	2. Femur consists of long, stout curved shaft. The femur gives support to the thigh region.
3. The proximal end of the shaft bears a rounded smooth head which fits info the acetabulum. There are also distinct prominences lesser trochanter and greater trochanter near the head.	3. The proximal end of femur is produced into a rounded head for the articulation with the acetabulum. Opposite to the head a small protuberance greater trochanter is present.	3. The proximal end of femur bears a rounded knob-like head which fits into the acetabulum. There are three rough projections greater, lesser and third trochanters present near the head. Lesser trochanter lies behind the head, greater trochanter in the middle line and the third trochanter opposite to the head are seen.
4. It is absent.	4. There is an articular surface is present between the head and trochanter for the antitrochanter of ilium.	4. It is absent.
5. Two knob-like condyles are present at the distal end of thefemur. These articulate with the tibia of the shank. Intercondylar groove is present between the two condyles. Patella is absent.	5. The distal end of femu has two prominent condyls with a intercondylar groove. Patella slides in the intercondylar groove on the anterior side. It is a disc-like sesmoid bone.	5. The distal end of femur is pulley-like having two condylesfor tibio-fibule which are separated by a patellar groove. A large sesmoid bone called the patella slides in the patellar groove. It is attached to the tibia by a ligament. Patella is present at the knee-joint.
6. The shank consists of two long bones - the tibia and the fibula. They are separate bones.	6. Tibiotarsus fibula is formed of tibiotarsus and fibula. They are separate bones.	6. Tibiofibula is formed of tibia and fibula. They are separate bones.
7. Tibia is a stout and curved bone present on the inner side. Its proximal end bears two concave facets for the articulation with the femur. It has also a longitudinal ridge the cnemial crest on the side. Tibiotarsus is absent.	7. Tibiotarsus is a large straight and stout bone and also longer than fibula. It is formed by the fusion of tibia and proximal row of tarsals. The proximal end of it bears a pair of articular surfaces for the condyles of the femur and in between them the cnemial crest for the attachment of tendon of extensor muscles.	7. Tibia is stouter towards the anterior end and narrow towards the posterior end. Its proximal end bears two concave facets for the articulation with the femur and distinct cnemial crest on side.
8. Tibia distally bears a concavity for the tarsals.	8. Tibio tarsus distally bears a pulley-like articular surface for the tarsals which is surrounded by a pair of distal lateral tubercles.	8. Tibia distally bears articular surface for the tarsals.
9. Fibula is a slender bone present on the outerside. It bears facets on either side.	9. Fibula is small, slender bone. It is closely applied to the tibiotarsus.	9. Fibula is a slender and weak bone. It lies on the outer side. The bone is narrower towards the distal end and is closely applied to the tibia.
10. Tarsab are five in number which are arranged in two rows. Proximal row has two tarsals the larger compound piece formed by the fusion of a rjbiale, intermedium and centrale and present infront of tibia. A small fibulare present infront of the Sbula. The distal row has three small tarsab called distal tarsab or distalia.	10. The free tarsals are absent. The proximal row of tarsals are fused with tibia and forms tibiotarsus. The distal row of tarsals are fused with the metatarsals and forms tarso metatarsus. It is as long as the femur bone. It is straight and stout.	10. There are six tarsal bones which are arranged in two rows. The proximal row tarsab are two, astragalus and calcaneum. Astragalus is considered to represent two fused tarsals. Calcaneun is produced back wards into a strong calcaneal process which forms the heel. The central row has only one tarsal-centrale or navicular. The distal row contains three tarsab. The first distal tarsal is absent due to the absence of hallux. The second distal tarsal is mesocuneiform which is the smallest distal tarsal. The third distal tarsal is ecto cuneiform which largest one. The fifth distal tarsals are fused to form largest bone in the row - cuboid.
11. There are five meta-tarsals corresponding to the five toes.	11. There are four meta tarsals. The first one is free and in the form of a small projection. The second, third and fourth are fused with the distal row of tarsals to form tarso metatar­sus. Ankle joint is known as mesotarsal.	11. There are four meta tarsals. There are second, third, fourth and fifth, meta tarsals. The first one is absent
12. There are five toes. There are two pha­langes in the hallux, three in the second, four in the third, five in the fourth and three in fifth toes. The pha­langes formula can be expressed as 2, 3, 4, 5, 3 (same as for the hand). The terminal phalanx of each toe supports a strong, curved, horny & pointed claw.	12. There are four toes. The hallux is directed backwards and contain two phalanges. The second toe with three, third one with four and the fourth one with five phalanges are formed. The phalanges formulae can be ex¬pressed 2, 3, 4, 5. The terminal phalanx of each toe is pointed and curved which supports a strong, pointed horny claw.	12. There are four toes. Each toe has three phalanges. The phalanges for­mula can be ex­pressed as 3, 3, 3, 3. The terminal part of each phalanx is pointed and curved to support a horny claw.