CHAPTER I
INTRODUCTION
A. Background
Chondrichtyhes class of vertebrates, sharks and their relatives, in cartilaginous fish called because they are relatively flexible has endoskeleton made of cartilage rather than bone from the bone hard. Cartilaginous skeleton of these fish were obtained characteristic, not characteristic of primitive, in other words Chondichtyes ancestors had bony framework, and cartilaginous framework which are characteristic of the class was developed afterwards. During the development of most vertebrates, was first composed of cartilage framework later becomes hard as the bones begin replacement of the soft cartilage matrix with a hard matrix of calcium phosphate. Apparently, some modification in the process of preventing the development of cartilaginous fish, the turnover process.