The<unk>  also known as the tunica adventitia, is the outermost layer of a blood vessel, surrounding the tunica media. It is mainly composed of collagen. The collagen serves to anchor the blood vessel to nearby organs, giving it stability.
A common pathological disorder concerning the<unk> is scurvy, also known as vitamin C deficiency. Scurvy occurs because vitamin C is essential for the synthesis of collagen, and without it, the faulty collagen cannot maintain the vein walls, and they rupture, leading to a wide multitude of problems.
Tunica externa 
Chordae tendineae
Tunica intima
Musculi pectinati
Anterior crural intermuscular septum
Transverse intermuscular septum
Cutis verticis gyrata
Crural fascia