SKELETON OF THE FORE LIMBS IN LIZARD, BIRD AND MAMMAL - COMPARATIVE ANOTOMY

FORELIMB SKELETON OF –REPTILE (LIZARD-CALOTES), BIRD-(PEGION-COLUMBA) AND MAMMAL-(RABBIT-ORYCTOLOGUS.)-SIMILARITIES-DIFFERENCES

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

A typical tetrapod fore limb can be divided into three segments. The upper arm, fore arm and hand (menus) are the three segments. As there are five fingers normally, this type of limb is known as pentadactyl limb.

The skeletal structures of the fore limb consists of humerus, radius ulna, carpals, Meta carpals and phalanges.

The humerus is the bone of the upper arm and its head articulates with the glenoid cavity .Its distal end articulates with the ulna The Radius and ulna are the bones of the fore arm. They articulate with humerus proximally and distally with the carpals of the mist bones. The radius bears most of the body weight.

The hand can be divided into wrist, palm and digits (fingers). The wrist is supported by carpal bones which are arranged in rows. The palm is supported by the metacarpals. The metacarpals are followed by linear series of phalanges of the fingers The phalanges number vary from 1 to 5.

The first finger of the fore limb is called 'pollex or thumb' and the fifth finger is the 'minimus'.

Calotes (garden lizard)	Columba (Pigeon)	Oryctolagus (rabbit)
1. The bones of the fore limbs are humerus, radius, ulna, carpals,metacarpals and phalanges.	1. The bones of the fore limb are humerus, radius, ulna, car-pals carpometa-carpus and phalanges.	1.The bones of the fore limb are humerus, radius, ulna, carpals, meta¬carpals and phalanges.
2. Humerus is in the form of a long bone with proximal and distal ends	2 Humerus is a long & slightly flattened with a bent shaft associated by proxi¬mal and distal ends.	2.Humerus possess a proximal head, shaft and a distal end.
3. The proximal end of humerus is round and distal end is pulley like with two articular surfaces for the radius and ulna. Supra trochlear foramen is absent.	3. The proximal end of humerus is highly expanded and form into the head A prominent deitcid ridge and a pneu¬matic foramen are present near the head. The distal end articulates with the radius and ulna by the articular surfaces. Supra trochlear fora¬men is absent.	3 The proximal end of hu-merus is divided into two parts by a bicipital groove. One part has head which fits into the glenoid cavity. This part has lesser tuberosity. The greater tuberosity is present on the other part. Shaft is present along with deltoid ridge. The distal end has median and lat¬eral epicondyles. Pulley-like trochlea is formed at the distal end which articulates with ulna. Suprotrochlear foramen is present.
4,Two elongated and separate radius and ulna bones are present.	4. Same as in calotes.	4.. Same as in columba.
5.Radius is a slender bone. It has a styloid process and concavity for the carpalsdistally.	5. Radius is a straight and slender bone. It has a concavity for the articulation with humerus at the proxima end The distal end is convex.	5. Radius is small slen­der and slightly curved bone With a concavity at the proximal end. The distal end is flat.
6 Ulna is rod liket and stoutet than radiu; Proximally it has ole.cranon process to articulate with humerus. Distally it has a concavity for the articulation with carpals.	6. Ulna is stouter and longer than radius It is slightly curved. A cranon process to blunt olecranon pro-cess is present at the proximal end. The distal ends of radius & ulna articulate with carpometacarpus.	6. Ulna is a long and curved bone Proxim My it bears olecranon process and sigmoid notch for the articulation with the trochlear end of humerus. Epiphyses are present at the distal ends of radius & ulna for the articulation with carpals.
7. Wrist or carpus has ten (10) small bony carpals arranged in three rows. The proximal row has three carpals - radiale, intermedium and ulnare. A centrale lies in the second row. A pisi­form is attached to the distal end of the ulna on its post axi­al side as an addi­tional bone. The third row has five distal carpals. Ex­cept the fourth, the remaining distal carpals are very small.	7. The wrist contains only two proximal carpals. One smaller-radiate and a larger ulnare articulate with radius & ulna respec­tively. The three dis­tal carpals are fused with the meta carpa­ls to form the carpometa carpus. It is a characteristic feature of aves.	7. Wrist consists of eight small carpal bones arranged in two rows. The proximal row contains three carpals-radiale or scaphoid, intermedium or semilunar and ulnare or unciform. The median row has a sin¬gle centrale. The distal row comprises four true carpals-trapezium, trapezoid, smallest magnum and largest unciform.
8 Carpometa carpus is absent Five slen­der meta carpals support the palm. These are of unequal size & with expanded ends. The middle or third meta carpal is the longest, the second and fourth are only a little shorter than the third. The first and fifth meta carpals are much shorter.	8 Meta carpals are three in number which are fused with the distal carpals and form an elongated compound bone carpometa carpus.	8. There are five long, slender and of unequal size metacarpals support the palm. The first is the shortest and the third is the longest. Each meta carpal has small epiphysis at their end with a middle slender shaft. Carpometa carpus is absent.
9. There are five fingers.	9. There are three fingers.	3. There are five fin­gers.
10 The phalanges are the small bones sup­port the fingers. The number of phalanges differ in the respec­tive fingers. The first finger has two, sec­ond has three, third has four, fourth has five and fifth has three phalanges Thus the phalanges formula can be ex­pressed as 2,3, 4, 5, 3.	10. The phalanges are the small bones sup­port the fingers. The first finger has one, second has two and third has one phalan­ges. Thus the phalan­ges formula can be expressed as 1, 2, 1.There are no claws on the fingers.	10. The phalanges are small bones and their total number is 14. The first finger has two phalanges & the remaining four fingers have three phalanges each. Thus the phalanges formula can be expressed as 2,3,3,3.3.
11. Sesamoid bones are absent The distai phalanx of each finger supports a strong curved, pointed claw is formed from the epidermis.	11.Sesamoid bones are absent.	11. Sroas nodule -like S ui .o . bones are | present on the underside of the fingers. These are seen at the joints between the meta carpals and the first phalanges and also between the second and third phalanges These pro¬vide additional strength to the fingers during bur¬rowing.
12. It is a penta dactyl limb.	12. The fore limb supports the wing.	12. it is a penta dactyl limb.

previous topic is about-PELVIC GIRDLE of vertebrates-comparative anatomy.