The myology of salamanders with particular reference to Dicamptodon ensatus (Eschscholtz). I. Muscles of the head

This paper is the first of a series of four describing the anatomy and development of the muscles of Dicamptodon ensatus (Ambystomidae) and comparing them in detail with those of other genera and families of Urodela. In the present paper the muscles of the eye, jaw and hyobranchial apparatus are included, with the exception of the few longitudinal throat muscles derived from trunk myotomes; the second paper will include those of the trunk and tail and their derivatives; the third, those of the limbs and the fourth, a discussion of developmental principles in myology and the bearing of muscles upon classification and phylogeny in the salamanders. The correlation of data on various larval, perennibranchiate and adult forms reduces many muscle names to synonymy, and simplifies the understanding of certain difficult parts of the anatomy. Less attention is given to innervation than to developmental changes and the derivation of the muscles. Dicamptodon, in the larval stage, typifies other larval and most perennibranchiate forms, at metamorphosis it shows the most generalized methods of muscular and skeletal transformation, and when adult the animal serves as a landmark for recognizing the directions of evolution among other Urodela.