The alveolar process is the lining of the tooth socket or alveolus (plural, alveoli). Although the alveolar process is composed of compact bone, it may be called the cribriform plate because it contains numerous holes where Volkmann's canals pass from the alveolar bone into the PDL. The alveolar bone proper is also called bundle bone because Sharpey fibers, a part of the fibers of the PDL, are inserted here. Similar to those of the cemental surface, Sharpey fibers in alveolar bone proper are each inserted at 90 degrees, or at a right angle, but are fewer in number, although thicker in diameter than those present in cementum. As in cellular cementum, Sharpey fibers in bone are generally mineralized only partially at their periphery.