part of part of bony projection cleithrum zone of bone organ postbranchial lamina Medial facing projection or surface on the anterior ( cranial) region of the cleithrum that is often textured or denticled. This process has two primary functions: 1) its shape enhances the vertical strength of the cleithrum and 2) it forms the edge of the gill chamber and helps to direct water after it has passed over the gills (modified from Clack 2012). UBERON:4200016 T Alexander Dececchi