HYOBRANCHIAL APPARATUS OF SPELERPES 533 



each of the three families of Urodeles that undergo complete 

 metamorphosis. Thus, among the Plethodontidae, Desmog- 

 nathus fusca, Typhlomolge rathbuni,^ and Spelerpes ruber and 

 bislineatus; among the Salamandridae, Triton taeniatus and 

 cristatus, Salamandra maculosa, and Diemyctylus viridescens, 

 and among the Amblystomidae, Amblystoma opacum and 

 punctatum, and the axolotl, all have this fusion of the cartilages. 

 Had time and material permitted my carrying this investigation 

 further, I have no doubt T should have found similar results 

 throughout the group, for the plate seems to have an important 

 physiological function in these larvae, serving for the basis of 

 attachment of powerful muscles which have to do with changes 

 of position of much of the hyoid region, including movements of 

 the lower jaw. 



2. Hyohranchial muscles 



The hyobranchial muscles of the Spelerpes larva correspond 

 rather closely to those of other larval Urodeles, including such 

 forms as Necturus. They are shown from the ventral aspect in 

 figure 6 and in sections, figures 7 to 16. 



The most superficial are the intermandibulares anterior and 

 posterior. These are thin, sheet-hke muscles which cover the 

 whole ventral surface of the lower jaw just beneath the skin. 

 The former extends between the two halves of the anterior three- 

 fourths of the mandible; the latter, in its attachments, is rather 

 more complex, as it takes some fibers from the mucous membrane 

 of the pharynx, some from the lateral edge of the distal end of 

 the ceratohyal, some from a fascia which covers the ceratohyoid- 

 eus externus muscle, and some from the midventral surface of 

 the distal end of the first epibranchial, on both sides. 



In young larvae there is but little indication of the median 

 raphe separating the two halves, which is present in metamorphic 

 specimens and adults (see below) as it is in most Urodeles. Out 



^ Stejneger and Barbour ('17) do not include Typhlomolge among the Pletho- 

 dontidae. The presence of the plate seems to me, however, to be only an ad- 

 ditional proof that this animal is in reality a larval Spelerpes, as Miss Emerson 

 so clearly shows ('05). 



JOURNAL OF MORPHOLOGY, VOL. 33, NO. 2 



