In your body, you have only two types of bone tissue: cortical and cancellous bone. In this lesson, we will learn about the structure and function of cancellous bone, which plays a crucial role in producing blood cells and stem cells and is the primary tissue affected by osteoporosis.
balaclava (plural balaclavas) 1  A warm cap shielding the neck and head, often made out of wool. ( 2 chiefly Canada) A ski mask with holes for the eyes and, sometimes, the nose and mouth, which may be rolled up and worn like a toque or pulled over the face for greater protection.
A mask is an object normally worn on the face, typically for protection, disguise, performance, or entertainment. Masks have been used since antiquity for both ceremonial and practical purposes. They are usually worn on the face, although they may also be positioned for effect elsewhere on the wearer's body.