Endoskeleton in Vertebrates | Zoology Optional Notes for UPSC PDF Download

Endoskeleton in Vertebrates: Chordata

Overview: The vertebrate skeleton serves as a vital framework for the body, providing support, protection, and a surface for muscle attachment. It can be categorized into dermal bony structures and the endoskeleton.

Dermal Bony Skeleton

1. Composition:
   • Consists of dermal scales, fin rays in fishes, and bony dermal plates in certain fossils (ostracoderms, placoderms, amphibians).
   • Forms bony armor (plates and scutes) in various species like sturgeons, turtles, crocodilians, and some mammals (e.g., armadillos).
2. Integration with Endoskeleton:
   • Distinction between dermal exoskeleton and endoskeleton is somewhat artificial as dermal bones contribute to the endoskeleton formation.

Endoskeleton

1. Development:
   • Originates from mesenchyme, initially forming cartilage in the embryonic stage, which is later replaced by bone in adults.
   • Bones developed in place of existing cartilages are termed cartilage or replacing bones. Those developing in the dermis are dermal or membrane bones.
2. Axial and Appendicular Skeleton:
   • Axial Skeleton: Skull, vertebral column, ribs, sternum.
   • Appendicular Skeleton: Pectoral and pelvic girdles, paired limbs, and unpaired appendages.
   • Visceral skeleton supports jaws and gills in fishes, contributing to the skull and hyoid in higher forms.
3. Functions:
   • Framework for body support.
   • Permits growth, maintaining a definite shape.
   • Provides protection to vital organs.
   • Offers surface for muscle attachment via tendons.
   • Bone marrow produces blood corpuscles.
   • Ear ossicles aid in hearing; tracheal rings and ribs assist in breathing.
4. Adaptations for Land Transition:
   • Limbs function as levers for locomotion and lifting the body.
   • Vertebral column acts as a rigid axis to support the head and resist limb thrust.

Specialized Functions

1. Bone Marrow:
   • Yellow marrow stores fats; red marrow (myeloid tissue) in mammals forms erythrocytes, blood platelets, and granular leucocytes.
   • Mammals have red marrow in embryos, later replaced partially by yellow marrow.

Understanding the functions and adaptations of the endoskeleton provides insights into its crucial role in vertebrate structure, support, and survival.