lower limbs are thicker and stronger than the upper limbs. The three segments of each lower limb are the thigh , the leg or the shank and the foot . The femur is the single bone of the thigh. It is the largest, longest and strongest bone in the body.
The head of femur articulates with the acetabulum of the pelvis to form the hip joint. Two parallel bones, the tibia and fibula , form the skeleton of the shank. A thick, triangular patella forms the knee cap, which protects the knee joint anteriorly and improves the leverage of thigh muscles acting across the knee. The foot includes the bones of ankle, the tarsus , the metatarsus and the phalanges or toe bones .
The foot supports our body weight and acts as a lever to propel the body forward, while walking and running. The tarsus is made up of seven bones called tarsals. The metatarsus consists of five bones called metatarsals. The arrangement of the metatarsals is parallel to each other.
There are phalanges in the toes which are smaller than those of the fingers. Structure of a Typical Long Bone A typical long bone has a diaphysis , epiphyses (singular-epiphysis) and membranes (Figure . ). A tubular diaphysis or shaft, forms the long axis of the bone.
It is constructed of a thick collar of compact bone that surrounds a central medullary cavity or marrow cavity . The epiphyses are the bone ends. Compact bone forms the exterior of epiphyses and their interior contains spongy bone with red marrow. The region where the diaphysis and epiphyses meet is called the metaphysis .
The external surface of the entire bone except the joint surface is covered by a double- layered membrane called the periosteum . The outer fibrous layer is dense irregular connective tissue. The inner osteogenic layer consists of osteoblasts (bone- forming cells) which secrete bone matrix elements and osteoclasts (bone-destroying cells). In addition, there are primitive stem cells, osteogenic cells, that give rise to the osteoblasts.
The periosteum is richly supplied with nerve fibres, lymphatic vessels and