chapter  10
Pectoral and Forelimb Muscles of Limbed Amphibians and Reptiles
Pages 62

The levator scapulae is not present as a distinct muscle in birds (Tables 10.1-10.2). As noted by Hetherington and Tugaoen (1990), in urodeles such as Ambystoma the muscle that is often named ‘opercularis’ clearly corresponds to part of the levator scapulae sensu this volume, which, in anurans such as Rana, is completely differentiated into two distinct muscles, the levator scapulae superioris and the opercularis sensu this volume (Tables 10.1-10.2). Therefore, the name opercularis should only be used for anurans (according to Carroll 2007, it is possible that the last common ancestor of all caecilians had a levator scapulae extending from the margin of an ‘operculum’-like structure to the suprascapula, but this muscle is missing in extant caecilians). Piatt (1938), based on his developmental study of Ambystoma, suggested that the levator scapulae of this taxon derives from somites 2-4, together with the hypobranchial muscles. The recent ontogenetic work of Piekaski and Olsson (2007) indicated, in turn, that in Ambystoma the levator scapulae derives mainly from somite 3, being innervated by the fi rst spinal nerve and also by the nerve hypoglossus, which is somewhat unexpected because this latter nerve is effectively usually associated with the hypobranchial muscles (see, e.g., Chapters 2-7). However, Piekaski and Olsson (2007) did show that the development and innervation of the levator scapulae are different from the innervation and development of the branchial muscle protractor pectoralis (‘cucullaris’), thus contradicting that the levator scapulae of urodeles derives from the protractor pectoralis, as was

often suggested in the older literature (for more details about this subject, see Piekaski and Olsson 2007).