Handbook of General Anatomy - Skeleton PDF

## Handbook of General Anatomy - Skeleton ### B. Developmental Classification 1. **Membrane (dermal) bones:** Ossify in membrane (intramembranous or mesenchymal ossification), and are thus derived from mesenchymal condensations. Examples: Bones of the vault of skull like frontal, parietal and faci...

## Handbook of General Anatomy - Skeleton ### B. Developmental Classification 1. **Membrane (dermal) bones:** Ossify in membrane (intramembranous or mesenchymal ossification), and are thus derived from mesenchymal condensations. Examples: Bones of the vault of skull like frontal, parietal and facial bones like maxilla (Fig. 2.1a). 2. **Cartilaginous bones:** Ossify in cartilage (intracartilaginous or endochondral ossification), and are thus derived from replacement of preformed cartilaginous models. Examples: Bones of limbs like humerus, femur, vertebral column and thoracic cage (Fig. 2.1b). 3. **Membrano-cartilaginous bones:** Ossify partly in membrane and partly in cartilage. Examples: Clavicle (sternal end ossifies by endochondral ossification while the rest of the bone ossifies by intramembranous ossification) (Fig. 2.4), mandible, occipital, temporal, sphenoid. 4. **Somatic bones:** Most of the bones are somatic. 5. **Visceral bones:** These are a few and develop from pharyngeal arches. Examples are hyoid bone, part of mandible (Fig. 2.1a) and ear ossicles (Fig. 2.12). ### C. Regional Classification 1. **Axial skeleton:** Includes skull, vertebral column, and thoracic cage (Fig. 2.1a). 2. **Appendicular skeleton:** Includes bones of the limbs, e.g. pectoral girdle, free upper limb and pelvic girdle, free lower limb (Fig. 2.1b). ### D. Structural Classification 1. **Macroscopically,** the architecture of bone may be compact or cancellous (Fig. 2.13). - **Compact bone** is dense in texture like ivory, but is extremely porous. It is best developed in the cortex of the long bones. This is an adaptation to bending and twisting forces (a combination of compression, tension and shear). - **Cancellous or spongy or trabecular bone** is open in texture, and is made up of a meshwork of trabeculae (rods and plates) between which are marrow containing spaces. The trabecular meshworks are of three primary types, namely: - a. meshwork of rods, - b. meshwork of rods and plates, and - c. meshwork of plates. - Cancellous bone is an adaptation to compressive forces. Bones are marvellously constructed to combine strength, elasticity and lightness in weight. Though the architecture of bone may be modified by mechanical forces, the form of the bone is primarily determined by heredity (Table 2.1). | Location | Compact bone | Cancellous (spongy) bone | |----------------|---------------------------------------------------------------------------|------------------------------------------------------------------------------| | Lamellae | In shaft (diaphysis) of long bone | In the epiphyses of long bone | | | Arranged to form Haversian system | Arranged in a meshwork, so Haversian systems are not present | | Bone marrow | Yellow which stores fat after puberty. It is red before puberty | Red, produce RBCs, granular series of WBC and platelets | | Nature | Hard and ivory like | Spongy | An image of the bones of the ear is included. The image is labelled "Fig. 2.12: Visceral bones- ear ossicles with their joints". The label is located at the bottom center below the image. The image shows the three bones of the middle ear: the malleus, incus, and stapes. Each bone is labelled and the joints between the bones are indicated. An image of a long bone is included. The image is labelled "Fig. 2.13: Structure of bone". The label is located at the bottom center below the image. The image shows the different parts of a long bone: the cancellous/spongy bone, compact bone, and medullary cavity.