Collagen , in the form of elongated fibrils , is mostly found in fibrous tissues such as tendon , ligament and skin , and is also abundant in cornea , cartilage , bone , blood vessels , the gut , and intervertebral discs . Collagen , in the form of elongated fibrils , is mostly found in fibrous tissues such as tendon , ligament and skin , and is also abundant in cornea , cartilage , bone , blood vessels , the gut , and intervertebral disc .