The Sacrum Bone is a triangular-shaped bone at the base of the spine. It is initially composed of five separate sacral vertebrae, which fuse by early adulthood.
The sacrum is curved longitudinally, and its two surfaces are concave anteriorly and convex posteriorly. Its middle part is crossed by four transverse ridges, which correspond to the original planes of separation between the five sacral vertebrae.
Scapula
The scapula, also known as the shoulder blade, is one of two large Sacrum Bone that make up the shoulder girdle in vertebrates. It is triangular in shape and sits on the back of the body between the levels of the second and eighth ribs.
Supraspinous & Infraspinous Fossae
The bone has a prominent spine that divides it into supraspinous and infraspinous fossae. This provides attachment sites for many muscles that play a role in moving the arm.
The scapula has an inferior angle that is covered by the latissimus dorsi muscle, which moves the arm forward round the chest when it is abducted. At the lateral part of the scapula is a deep notch, the scapular notch, which is formed partly by the base of the coracoid process and is converted into a foramen by the superior transverse scapular ligament; this serves as the passage of the suprascapular nerve.
Lumbar Spine
The lumbar spine is the largest section of your spinal column. It consists of five vertebrae that support the weight of your body and allow you to move your trunk.
The vertebrae are separated by a rubbery pad that protects them from grinding against one another and creates small spinal joints called intervertebral discs. These discs also act as a shock absorber to cushion impact.
Bony Enclosure
These vertebrae provide a bony enclosure for your spinal cord and the “tail” of nerves that descend from the end of your spinal cord (the cauda equina). They control your legs, bowel and bladder.
When you are born, your lumbar spine may be composed of only five vertebrae or it may include a sixth vertebra. When this happens, it’s called a transitional vertebra.
Pelvic Girdle
The pelvic girdle is a ring-like bony structure that connects the axial skeleton to the lower limbs. It is formed by the right and left hip bones, the Sacrum Bone and the coccyx.
Each of the hip bones is made up of three sections – ilium, ischium and pubis. At puberty, these sections fuse to form one Sacrum Bone.
Abdominal & Pelvic Viscera
These bones support the body, transfer weight between the axial and appendicular skeletons, and protect the abdominal and pelvic viscera. They also allow muscle attachment for muscles of the trunk and lower limbs, and serve as a transfer site between the upper and lower body.
The ilium is the largest bone of the pelvic girdle, while the ischium and pubis are smaller. These bones provide attachment sites for most of the proximal lower limb muscles, including adductor magnus, long head of biceps femoris, semitendinosus and quadratus femoris. They also give attachment to the piriformis, coccygeus and levator ani muscles.
Femur
The femur (Latin for thigh bone) is the largest and strongest bone in tetrapod vertebrates. Its proximal end articulates with the acetabulum of the pelvic bone, forming the hip joint, and its distal end forms the knee joint with the tibia and patella (kneecap).
The shaft of the femur is long and cylindrical in cross section. The anterior surface is convex and bound by lateral and medial rounded borders. The posterior surface has roughened ridges called the linea aspera. These ridges split and form the medial and lateral supracondylar lines.
Final Words:
The femoral head projects medially and superiorly to articulate with the acetabulum of the ilium, ischium, and pubic Sacrum Bone. Immediately lateral to the head is the neck of the femur, which narrows to allow greater range of motion at the hip joint. This neck is angled superomedially to accommodate the femoral head in the acetabulum and to align with the mechanical axis of the femur.