Musculus Biceps in Testudines, with Special Reference to Its Variation in the Family Bataguridae

Abstract

Walker (1973), while reviewing the previous studies on the muscular morphology of turtles (e.g., Hoffmann, 1890; Ashley, 1955; Zug, 1971), examined the pectoral muscles of five cryptodiran and two pleurodiran species, and recognized two types of M. biceps in Testudines. This muscle, one of the ventral muscles of the pectoral girdle and brachium, arises from posterior border of the coracoid and acts on the forearm. One of the two types of M. biceps recognized by Walker consists of two distinct elements, Mm. biceps superficialis and biceps profundus, whereas the other, showing no such division, is morphologically and topologically similar to M. biceps profundus of the forrotas (CFBH 412-416); Itatinga (DZSJRP 1841-1843, 845); Itapeva (MZUSP 60866); iraju (MNRJ 17225); irassun nga (MNRJ 17242-17246; MZUSP 91001 3; 14450-14471; 30983-30984); Sao Paulo (MZU P mer. Walker (1973) listed Bataguridae, Carettochelyidae, Chelydridae, Emydidae, Trionychidae, Chelidae, and Pelomedusidae as having divided M. biceps, and Cheloniidae, Dermochelyidae, and Testudinidae as having an undivided one. For Dermatemydidae, Kinosternidae, and Platysternidae, he provided no information regarding the condition of the M. biceps. According to Walker (1973), in the superfamily Testudinoidea, Testudinidae has a single M. biceps, whereas Bataguridae and Emydidae have a double M. biceps. Our preliminary examinations, however, showed that a batagurid species, Mauremys japonica, has a single M. biceps (see below). In Walker's (1973) study, most families were represented by small numbers of species, and the intrafamilial variation in M. biceps morphology was scarcely considered. We thus extended our investigations of the M. biceps variation to a number of other batagurid species. To explore comparative data and to confirm Walker's (1973) results, we also examined several representatives of other families.