part of part of subdivision of skeleton fin skeleton mesomere (fin) The median series of bones supporting the pectoral fin of sarcopterygian fish. See Dipnomorpha. In the pectoral fin, the first mesomere is the humerus, the second the ulna, and the third probably the intermedium. The radius is the first preaxial radial. All other homologies are suspect. from http://palaeos.com/vertebrates/glossary. UBERON:4200160