Pectoral Girdle of a Frog

The pectoral girdle is responsible for supporting the forelimbs and protecting the inner organs, foremost of which are the lungs and heart. It is made up of bones and cartilages that provide a foundation for attachment of muscles which are involved in the movement of the forelimb. Amphibians like frogs have a very distinct pectoral girdle compared to other vertebrates. This is because their mode of locomotion requires swimming as much as they require jumping.

1.0Main Functions of the Pectoral Girdle in Frogs

• Support of Forelimbs: The pectoral girdle provides structural support of the forelimbs for the movement and stabilization of the body of the frog.
• Shock Absorption: When a frog jumps, the pectoral girdle takes shock upon landing. Thus, it protects internal organs.
• Respiration Support: The pectoral girdle helps in the movement of the rib cage, assisting the frog's respiratory system.

2.0Pectoral Girdle Anatomy of Frogs

In a frog, there are three basic components on the side that help to form the pectoral girdle

1. Suprascapula
2. Scapula
3. Clavicle
4. Coracoid

These structures are bound together by cartilage and ligaments thus forming a functional unit.

1. Suprascapula

• Location: It's a flat wide and cartilaginous structure lying dorsally on the upper side of the body.
• Position: The suprascapula helps in the support of the muscles of the forelimb. When the frog lands, it helps absorb the shock upon falling.

2. Scapula

• Position: It is a small, bony plate that lies ventrally to the suprascapula. It is the limb attachment.
• Role: It attaches and connects the muscles to the forelimbs. It allows limb movement and strength.

3. Clavicle

• Positioning: Paired, rod-like bones are positioned anteriorly.
• Function: The clavicles support the pectoral girdle and distribute forces from the forelimb during locomotion.

4. Coracoid

• Positioning: Paired, rod-like bones located ventrally, below the scapula.
• Function: The coracoid bones contribute to the suspension of the chest and serve as a point of attachment for muscles that contribute to the movement of limbs. The integrity of the pectoral girdle is crucial to jumping movements, as these bones must bear the tension.

3.0Other Supporting Structures

1. Sternum (Breastbone): The sternum runs parallel to the coracoid bones and, with them, forms the girdle complex, thus supporting the girdle.
2. Procoracoid Cartilage: Just in front of the coracoid, this cartilage provides further flexibility and mobility in the girdle.

4.0Types of Pectoral Girdle in Frogs

There are two forms of pectoral girdle in frogs:

1. Firmisternal Type

• In this instance, the coracoids are firmly attached to the sternum.
• The girdle becomes much stiffer so that there is more support and strength during the movement.
• Common in frogs that make a very powerful jump.

2. Arciferal Type

• Coracoids in this kind are weakly fixed and can also overlap.
• This provides flexibility and range of motion, more often seen in swimming dependent or softer landing frogs.
•  It is common in those species that require flexibility and minimal solidity for movement.

5.0Evolutionary Adaptations of the Pectoral Girdle in Frogs

• Jumping Adaptation: Frogs developed the pectoral girdle to bear the impact of landing after a great jump. The suprascapula and other parts help to distribute the force all around the body.
• Swimming: Frogs' pectoral girdles are designed to allow flexibility for swimming efficiently. The arciferal type of girdle provides the required mobility to swim through an aquatic environment.

6.0Comparison to Other Vertebrates

• Amphibians vs. Reptiles: As compared with reptiles, frogs have a far more cartilaginous pectoral girdle, so it is much more flexible. Reptiles usually have a more ossified girdle that gives greater support but little more flexibility.
• Adaptation for Dual Locomotion: Since frogs are amphibians, their pectoral girdle must be functional on land and in water; however, vertebrates have pectoral girdles that can be adapted specifically for one type of locomotion.

7.0Conclusion 

• The pectoral girdle of a frog is a complicated and adaptive apparatus supporting its locomotion, respiration, and body as a whole. 
• Its being made up of bones and cartilage enables it to either be rigid or flexible, depending upon which mode of movement is assumed by the frog - whether jumping or swimming. 
• Evolutionary adaptations in the pectoral girdle are very distinctive because frogs are amphibians; hence, making it a subject of study in vertebrate anatomy.