Anatomy of finfish and shellfish

Unit 10 - Skeletal system

10.1. Introduction
The skeletal system of vertebrates is composed of bone and/or cartilage. Bone tissue is found only in the Subphylum Vertebrata. Some of the lower vertebrates do not possess bone, but all the higher vertebrates do. As such, bone is often thought of as being typical of vertebrates. In vertebrates, bone functions as a supporting tissue, a calcium reserve and as a hemopoietic (blood forming) tissue.
The skeleton is the basis of form and support of the vertebrate body. Muscles attach to the skeleton and vital organs are surrounded and protected by skeletal elements. As you examine the skeletons of the perch and the rat you should note a number of basic changes that have occurred in the evolution of the vertebrate skeleton. Some of the changes involve a reduction in the number of bones in the skull and a reduction in the number of ribs. Correlated with the move from an aquatic to a terrestrial environment are the increase in the complexity of the limbs and limb joints, the development of the pectoral and pelvic girdles and the strengthening of individual bones to support the weight of the organism on land. The central structure of support in the lower vertebrates, the notochord, is progressively replaced functionally by elements of the vertebrae. Although the notochord runs the length of the vertebral column in fish, in many it has been greatly restricted by the vertebrae. In adult tetrapods, the only remnant of the notochord is the gelatinous material found in the intervertebral discs between successive vertebrae of the vertebral column.
In the study of the skeletal system in the perch and a more advanced vertebrate, the rat, you should try to determine which skeletal features are signs of typical evolutionary advancement and which may be specializations due to the animal’s way of life.
The skeleton of vertebrates is broadly divided into two parts: the axial skeleton consisting of the skull, vertebrae and ribs; and the appendicular skeleton consisting of the pectoral and pelvic girdles and the bones of the appendages.