FIGURE 7.7 • Diagram of cartilage matrices. Note the areas of capsular, territorial, and interterritorial matrices. The characteristics of each are described in the text above.
In early fetal development, hyaline cartilage is the precursor of bones that develop by the process of endochondral ossification (Fig. 7.8). Initially, most long bones are represented by cartilage models that resemble the shape of the mature bone (Plate 8, page 212). During the developmental process, in which much of the cartilage is replaced by bone, the remaining cartilage serves as a growth site called the epiphyseal growth plate (epiphyseal disc). This cartilage remains functional as long as the bone grows in length (Fig. 7.9). In a fully grown individual, the cartilage that remains from the developing skeleton is found on the articular surfaces of joints (articular cartilage) and within the rib cage (costal cartilages). Hyaline cartilage also exists in the adult as the skeletal unit in the trachea, bronchi, larynx, and nose.
A firmly attached connective tissue, the perichondrium, surrounds hyaline cartilage.
The perichondrium is a dense connective tissue composed of cells that are indistinguishable from fibroblasts. In many respects, the perichondrium resembles the capsule that surrounds glands and many organs. It also serves as the source of new cartilage cells. When actively growing, the perichondrium appears divided into an inner cellular layer, which gives rise to new cartilage cells, and an outer fibrous layer. This division is not always evident, especially in perichondrium that is not actively producing new cartilage or in very slow-growing cartilage. The changes that occur during the differentiation of new chondrocytes in growing cartilage are illustrated in Figure 7.4.
Hyaline cartilage of articular joint surfaces do not possess a perichondrium.
Hyaline cartilage that covers the articular surfaces of movable joints is termed articular cartilage. In general, the
FIGURE 7.8 • Photomicrograph of several cartilages that form the initial skeleton of the foot. The hyaline cartilage of developing tarsal bones will be replaced by bone as endochondral ossification proceeds. In this early stage of development, synovial joints are being formed between developing tarsal bones. Note that nonarticulating surfaces of the hyaline cartilage models of tarsal bones are covered by perichondrium, which also contributes to the development of joint capsules. Also, a developing tendon (T ) is evident in the indentation of the cartilage seen on the left side of the micrograph. 85.
structure of articular cartilage is similar to that of hyaline cartilage. However, the free, or articular, surface has no perichondrium. Also, on the opposite surface, the cartilage contacts the bone, and there is no perichondrium. Articular cartilage is a remnant of the original hyaline cartilage template of the developing bone, and it persists throughout adult life.
In adults, the articular cartilage is 2 to 5 mm thick and is divided into four zones (Fig. 7.10).
 The superficial (tangential) zone is a pressure-resistant region closest to the articular surface. It contains numerous
FIGURE 7.9 • Photomicrograph of the proximal end of a growing long bone. A disc of hyaline cartilage−the epiphyseal plate−separates the more proximally located epiphysis from the funnel-shaped diaphysis located distal to the plate. The articular cartilage on the surface of the epiphysis contributes to the synovial joint and is also composed of hyaline cartilage. The cartilage of the epiphyseal plate disappears when lengthwise growth of the bone is completed, but the articular cartilage remains throughout life. The spaces within the bone are occupied by marrow. 85.
condensation of type II collagen fibrils that are arranged in fascicles parallel to the free surface.