1. Scapula: The pectoral girdle consists of a pair of scapulae, which are flattened, triangular bones. The scapulae serve as the main structural components of the shoulder region and provide a surface for muscle attachment.
2. Coracoid: Each scapula is fused with a coracoid bone. The coracoid is a robust, rod-like bone that extends ventrally from the scapula and contributes to the formation of the shoulder joint.
3. Supraclavicle: The pectoral girdle also includes a pair of supraclavicles, which are small, rod-like bones located dorsal to the scapulae. They provide additional support and stability to the shoulder region.
4. Postclavicle: Another pair of bones called postclavicles is present in the pectoral girdle. They are located ventral to the scapulae and contribute to the formation of the shoulder joint.
5. Joints: The pectoral girdle forms several joints that allow for movement of the pectoral fins. The shoulder joint, formed between the scapula and the coracoid, enables the fin to move up and down. Additionally, the pectoral fins are connected to the body through the scapulocoracoid joint, which provides stability and allows for some limited movement.
6. Muscles: The pectoral girdle serves as the attachment point for various muscles that control the movement of the pectoral fins. These muscles include the levator fin, depressor fin, protractor fin, and retractor fin muscles, which work together to provide the necessary force and control for fin movement.
Overall, the pectoral girdle in dogfish sharks provides structural support for the pectoral fins, facilitates their movement, and enables the sharks to maintain their stability and maneuverability in the water.