Dictionary of Ichthyology
pectoral girdle = the bony support of the pectoral fin behind the gills and usually attached to the posterior part of the skull; the "shoulder" girdle. Composed of the following basic elements (some of which may be lost): coracoid, scapula, pterygials, postcleithrum, cleithrum (main bone), supracleithrum and posttemporal. The "primary" pectoral girdle includes actinosts, scapula, coracoid, and sometimes mesocoracoid cartilage or endochondral bones and supports the fins directly. The "secondary" (and more primitive) pectoral girdle encloses the dermal post-temporal, supracleithrum, cleithrum, and two postcleithra, which are membrane bones and is only indirectly related to the fins. Also called scapular girdle, shoulder girdle.