Human Anatomy Positions and Planes

Anatomical erect is the standard reference point, with the body standing upright, eyes forward, arms hanging, palms facing forward, and thumbs pointing laterally.
Supine describes lying on the back.
Prone describes lying on the face.
Lateral decubitus describes lying on the side, either right or left.
Lithotomy involves lying on the back with hips and knees flexed and hips abducted.

The median (sagittal) plane is a vertical plane that divides the body longitudinally into equal right and left halves.
Paramedian planes run parallel to the median plane.
The coronal (frontal) plane cuts the body vertically, dividing it into an anterior (front) and posterior (back) part.
The horizontal plane is a transverse plane that runs horizontally, dividing the body into superior (upper) and inferior (lower) parts.

Superficial fascia is loose connective tissue located immediately deep to the skin.
This layer allows the skin to move freely over underlying structures.
It contains varying amounts of fat, which is more abundant in females, particularly in the breasts, anterior abdominal wall, and gluteal region.
Fat is less abundant in the limbs and absent in the eyelid, penis, and scrotum.
Superficial fascia functions to soften and smooth the body surface, facilitate skin movement, prevent heat loss, conduct nerves, blood vessels, and lymphatics supplying the skin, contain muscles in the face, and contain glands like the mammary gland.

Deep fascia is a strong, inelastic membrane made of compact, regularly arranged collagen fibers.
It is well-defined in the limbs, especially strong in the palm and sole, and absent in the face and anterior abdominal wall.
Deep fascia forms broad sheets that surround muscle groups, fix underlying structures, provide attachment for muscles, and support venous return.
It also forms intermuscular septa and interosseous membranes that separate muscle groups with different actions and nerve supply, and increase surface area for muscle attachment.
Deep fascia forms retinacula, thickened transverse bands at the wrist and ankle that hold tendons in position.
It forms palmar and planter aponeurosis, thick, strong layers that protect vessels, nerves, and tendons.
Finally, it forms fibrous sheaths around large vessels like the carotid sheath in the neck, enclosing the carotid arteries, internal jugular vein, and vagus nerve.

The arrangement of deep fascia helps explain the path of infection spread, for example, from the floor of the mouth to the larynx.
Fluid accumulation in the superficial fascia leads to edema.
Skin mobilization after incision occurs at the superficial fascia plane, and skin incisions along skin creases tend to heal with minimal scarring.

Bones are hard types of connective tissue that form the skeleton.
They provide shape, protection for vital organs, surface area for muscle attachment and joint formation, support and weight transmission, and a site for blood cell production in bone marrow and calcium storage.
The skeletal system is divided into the axial skeleton, which includes the skull, mandible, hyoid, sternum, ribs, and vertebral column, and the appendicular skeleton, which includes the bones of the upper and lower limbs.

Ossification refers to the process of bone formation.
Intra-membranous ossification is the process where bone develops directly from connective tissue membrane (mesenchyme). This occurs in bones like the skull cap and clavicle.
Intra-cartilaginous ossification, on the other hand, involves the formation of cartilage as an intermediary structure before bone development. This occurs in most bones of the body.