The Epaxial Musculature of Siren, Amphiuma, and Necturus (Amphibia)

Abstract

Almost all of the studies dealing with the trunk musculature of urodeles have been restricted to the hypaxial series. In this study the epaxial muscle mass of three genera (Siren, Amphiuma, and Necturus) have been examined. The entire dorsal muscle mass is divided into three main units on the basis of fiber attachments. Each unit is in turn provided with several distinct fiber tracts, derived from a primitive and simple myoseptal system. These minor complexities are described in regards to approximate size, direction, and attachment in the three genera studied. All three genera have a similar arrangement in the more superficial fiber tracts. In regard to the deeper tracts Necturus is most primitive. Siren and Amphiuma illustrate certain specializations involved in allowing these genera to bend their body vertically to a greater extent than is normally possible in members of this class. The specializations are apparently independently derived. The abandonment of myoseptal attachments and intervertebral systems more well developed are examples of such specialization.