Comparative study of Forelimb bones of vertebrate

Forelimb Bones of Frog

Forelimb Bones of Frog are Humerus, radio-ulna and hand bones constitute bones of forelimb.

Comments :

• Humerus
  • It is a short, cylindrical and slightly curved bone of upper arm.
  • Proximal end fits into glenoid cavity of pectoral girdle. It is swollen forming head, which is covered by calcified cartilage.
  • Below head is a deltoid ridge for muscle attachment.
  • Distal end has a prominent trochlea or capitulum and a condylar ridge for articulation with radio-ulna.
• Radio-ulna
  • It is the compound bone of forearm formed by fusion of radius and ulna.
  • Proximal end contains a concavity for articulation with capitulum of humerus and an olecranon process.
  • A groove divides radius and ulna distally; each terminating into a facet to articulate with carpal bones.
• Bones of hand
  • Wrist bones are called as carpals, which are 6 in number and arranged in two rows of 3 each.
  • Bones of proximal row, namely radiale, intermedium and ulnare, articulate with radio-ulna.
  • Bones of distal row, namely trapezium, traezoid and capitohamatum. articulate with metacarpals.
  • First metacarpal is rudimentary and without a digit and phalanges. Besides metacarpals. digits are internally supported by short bony rods, known as phalanges. First and second digits contain two phalanges each, while third and fourth digits have 3 phalanges each.
  • Claws are absent.

Forelimb Bone of Varanus

Comments:

Forelimb Bone of Varanus is constituted by humerus, radius and ulna and bones of forefoot or hand.

• Humerus
  • It is upper arm, single bone, with both ends Expanded.
  • Proximal end contains head which fits into glenoid cavity.
  • The head and a medial process enclose a bicipital fossa.
  • Deltoid ridge present.
  • Distal end pulley-like and trochlea contains two articular facets for radius and ulna.
• Radius and ulna
  • Unlike frog, radius and ulna are not fused.
  • Radius is slender and made up of a shaft and two epiphyses. Distal end contains a concave articular facet and a pre-axial styloid process;
  • Ulna is stouter. Proximal end contains olecranon process and distal end has a convex articular surface for carpus.
• Bones of forefoot or hand
  • Wrist is made up of 10 small polyhedral rounded bony carpals arranged in two rows.
  • Proximal row contains three carpals, namely radiale, ulnare and intermedium.
  • Distal row has 5 carpals.
  • A central is found between two rows and a pisciform is attached to the distal epiphyses of ulna.
  • Manus contains five elongated metacarpals and bears 5 digits made up of 2. 3. 4, 5 and 3 phalanges, respectively.
  • Each terminal phalanx contains a horny claw.

Forelimb Bones of Fowl

The Forelimb Bones of Fowl is adapted for flight with the rcnllt radius and ulna do not move upon each other, distal carpals fuse with the metacarpals forming carpometacarpus and only three digits are present. Forelimb is composed of humerus, radius. ‘llna, carpals, carpometacarpus and phalanges.

Comments:

• Humerus
  • It is pneumatic upper arm bone expanded at both ends.
  • Proximal end contains a convex head, which bears one smaller pre-axial tuberosity or deltoid ridge for pectoral muscles and other greater post-axial tuberosity, which contains a large pneumatic foramen c.;ommunicating with air space in shaft of bone.
  • Distal end contains two trochlear articular surfaces for radius and ulna. Anterior view deltoid ridge condyles and intercondyler groove. Posterior view show, pneumatic foramen and olecranon fussa.
• Radius-ulna
  • Radius and ulna constitute separate bones.
  • Radius is straight and slender. Proximal end has a cavity for outer condyle of humerus, while distal knob-like end fits into radiale carpal.
  • Ulna is longer and curved. Proximal end contains a facet for inner condyle of humerus and is produced as olecranon process. Distal end articulates with carpals and radius. Ulna also has sigmoid notch and nutrient foramen.
• Carpals :- Radiale articulating with radius and ulnare articulating with ulna form proximal carpals.
• Carpo-metacarpus.
  • Three metacarpals fuse with distal row of carpals to form carpometacarpus.
  • First metacarpal is stumpy, second in the form of a straight bone and third slightly curved outwardly.
• Phalanges : Three digits only. Polex or first digit has a single phalanx, index or second digit has two phalanges, while third digit has only one phalanx.

Forelimb Bones of Rabbit

Forelimb Bones of Rabbit comprises of humerus, radius, ulna and bones of forefoot or hand.

Comments :

• Humerus.
  • It is a rod-shaped bone.
  • Head articulates with glenoid cavity.
  • Close to head are outer greater and inner lesser tuberosities and bicipital fossa.
  • Deltoid ridge present.
  • Distally humerus contains a pulley-like trochlea to articulate with ulna. (vi) Just above trochlea are coronoid and olecranon fossae.
• Humerus in posterior view shows bicipital fossa, lesser tuberosities, greater tuberosity, shaft, supratrochlear lumen head and trochlea.
• Radius and ulna (Side view).
  • Radius and ulna are separate but united firmly at both ends.
  • Radius is smaller and curved.
  • At the proximal end of ulna is an olecranon process which articulates with olecranon fossa of humerus.
  • At the base of olecranon process is a sigmoid notch which fits into trochlea of humerus.
• Bones of forefoot or hand.
• Wrist contains nine small bones in two rows, namely radiale, intermedium and ulnare in proximal row and single centrale, trapezium, trapeziod, magnum, and unciform in distal row.
• A sesamoid bone or pisciform is found on ventral side of carpus.
• Manus has five digits with 2, 3, 3, 3 and 3 phalanges, respectively.
• Terminal phalanx bears a horny claw.