Copyright Goodheart-Willcox Co., Inc. Chapter 5 The Skeletal System 125 marrow, which has a rich supply of blood vessels and acts as a storehouse for fat. The medullary cavity is lined by a membrane known as the endosteum. The bulbous ends of long bones are known as epiphyses. These regions are composed of trabecular tissue that contains red marrow, which participates in the formation of red blood cells (erythrocytes) and some white blood cells (leukocytes). Although all bone marrow is red at birth, only about half of the marrow is red by adulthood the other half is yellow. Epiphyses are also the sites of bone growth in long bones and continue to enlarge as a person ages, adding length to the bone. Each epiphysis is surrounded by a protective covering of articular cartilage. You may have noticed the shining white covering of articular cartilage over the ends of the bone in a chicken drumstick. How does living bone receive nourishment and get rid of waste products? Bone has what you might think of as its own subway system. An intricate array of passageways exists at a microscopic level inside the mineralized part of bone. Blood vessels and nerves having been formed by the attachments of tendons and ligaments, or providing reciprocally shaped articulations for blood vessels and nerves at joints or channels. The names of many of these surface features identify the locations of muscle attachments and other points of interest. Figure 5.5 lists and describes the general names of the anatomical surface features of bones. Anatomical Structure of Long Bones The diaphysis of a long bone is the hollow shaft composed of cortical bone (Figure 5.6). A fibrous connective tissue membrane called the periosteum surrounds and protects the diaphysis. Mats of tiny fibers composed primarily of collagen, known as Sharpey’s fibers, firmly bind the periosteum to the underlying cortical bone. The periosteum contains blood and lymph vessels, as well as nerves. It is involved in bone growth, repair, and nutrition. The hollow center of the diaphysis is the medullary canal, or cavity. Beginning when a person is about 5 years old, this cavity is filled with yellow bone Surface Anatomy of Bones Components of Joints Feature Description Example facet small, smooth articular surface facet joints of a vertebra condyle knob-like articular surface femoral condyles head prominent, expanded end of a bone head of a femur Projections Feature Description Example process any bony prominence transverse process of a vertebra trochanter process on the proximal femur greater trochanter of femur crest prominent, narrow bony ridge intertrochanteric crest of femur line slightly elevated, long, narrow ridge linea aspera of femur spine sharp, slender process spine of scapula tubercle small, rounded process adductor tubercle of femur tuberosity rough, elevated surface gluteal tuberosity of femur epicondyle elevation superior to a condyle femoral epicondyles neck column supporting a head femoral neck Depressions and Openings Feature Description Example fossa shallow depression supraspinous fossa of scapula sinus cavity or hollow filled with air sinuses of skull alveolus small hollow tooth socket foramen rounded opening foramen of the skull meatus opening into a canal external acoustic meatus (ear) canal tube-like passageway auditory canal in skull Figure 5.5 Goodheart-Willcox Publisher