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AUTHOR'S ABSTRACTThe development of the cranial musculature of Amblystoma punetaturn is described in detail, for both larva and adult. I n addition, a brief account of the innervation of each muscle is given. The study of normal development i s supplemented by extirpation experiments performed on embryos in early stages of development. These extirpations include the mesodermal head segments, mesoderm of mandibular hyoid second branchial, third branchial arches, and somites 1, 2 and 3. The eye huscles' are found to develop from the mesodermal head segments in precisely the same manner as in other classes of vertebrates; head segmentation of Amphibia though less accentuated is shown to be homologous with that of other classes. The redaining extirpation experiments corroborate, in general, the 5nding from normal development studies. An attempt is made to summarize in tabular form the prospective fate of the prechordal plate and parachordal mesoderm, the two earliest divisions of the head mesoderm, with regard to their complete muscle derivatives.'Revision of a dissertation presented in partial fulfillment for the degree of Doctor of Philosophy in Yale University. 531 532 JEAN PIATT adult. Careful comparison has also been made mitli rnanv other urodele species. It is beyond the scope of this paper to present this at the present time. Ho\wver, a brief account of the innervation of each muscle is given. This work is divided into nine sections. These divisions are largely the expression of a rational system of muscle grouping according to origins. However, various sections represent in part oiiljan obvious rubric for converiieiit classification. Xaterial and techiaique

ONE CHART AND FOUR PLATES (FIFTEEN FIQURES) AUTHOR'S ABSTRACTThe hyobranchial apparatus and throat musculature of the plethodontid salamanders are examined. The interhyoideus is thought to be the homologne of the intermandibularis posterior and the posterior part of the intermandibularis anterior. The quadrato-pectoralis is found only in Desmognathus (Leurognathus?), and Aneides. I t s presence in the former is a primitive condition: in the latter, secondary. The gularis had its phylogenetical ongin as a slip from the quadrato-pectoralis. The lingual cartilage is found only in Oyrinophilus, Pseudotriton, Eurycea, and Manculus. It is the homologue of the 'sehnenplatte' of Salamandra : not the otoglossal.the suprapeduncularis and the absence at the genioglossus in not peculiar to adult free tongued genera. The anatomical emdence allies Batrachoseps with Hydromantes and Oedipus. The latter two genera are derived from ancient Plethodon stock not from Oyrinophilus stock. Stereochilus, Typhlotriton, and Typhlornolge are the degkerate deacendanta from ancient Oyrinophilus stock.

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