Fibrous proteins are long, insoluble, and structural proteins that provide support and strength to tissues and organs. They are characterized by their elongated, fibrous shape, and their lack of tertiary and quaternary structure. Among the options given, collagen is the only fibrous protein.

Collagen:
- Collagen is the most abundant protein in the human body, accounting for approximately one-third of the body's protein content.
- It is a major component of connective tissues such as tendons, ligaments, skin, and cartilage.
- Collagen provides strength and support to these tissues and is responsible for their elasticity and flexibility.
- It is a triple helix structure consisting of three protein chains wound together.
- Collagen is rich in the amino acids glycine, proline, and hydroxyproline, which give it its characteristic strength.

Globulin:
- Globulins are a group of proteins that are soluble in water and salt solutions.
- They are involved in a variety of functions, such as transport of hormones and lipids, immune defense, and blood clotting.
- Examples of globulins include immunoglobulins (antibodies), transferrin (iron transport), and fibrinogen (blood clotting).

Haemoglobin:
- Hemoglobin is a protein found in red blood cells that is responsible for carrying oxygen from the lungs to the rest of the body.
- It is a complex protein consisting of four protein subunits, each containing a heme group that binds to oxygen.
- Hemoglobin is not a fibrous protein as it has a globular structure.

Hordein:
- Hordein is a type of protein found in barley grains.
- It is a storage protein that provides nutrients for the developing plant embryo.
- Hordein is not a fibrous protein as it has a globular structure.

In conclusion, collagen is the only fibrous protein among the options given, and it plays a crucial role in providing strength and support to various tissues in the body.