No extensive study of the muscular system was undertaken, but certain muscles know to be of taxonomic importance were studied.
_Jaw Musculature._--Starrett (1960) pointed out the unique jaw musculature in _Smilisca_. In this genus M. depressor mandibulae consists of two parts, one arising from the dorsal fascia and one from the posterior arm of the squamosal. Two muscles arise from the anterior arm of the squamosal and insert on the lateral face of the mandible. Of these muscles, M. adductor mandibulae posterior subexternus lies medial to the mandibular branch of the trigeminal nerve; the other, M. adductor mandibulae externus superficialis, lies lateral to the same nerve (Fig. 9). In most other hylids the latter muscle is absent. No significant variation in the position of the muscles was noted in the various species of _Smilisca_, though M. adductor mandibulae originate somewhat more anteriorly in _S. baudini_ and _S. cyanosticta_ than in the other members of the genus, all of which have a shorter anterior arm of the squamosal that does not reach the maxillary. The two separate parts of M. depressor mandibulae are not so widely separated in members of the _sordida_ group as in the _baudini_ group.
[Illustration: FIG. 9. Lateral view of the left jaw of _Smilisca baudini_; _A. M. E. S._, adductor mandibulae externus superficialis; _A. M. P. S._, adductor mandibulae posterior subexternus; _Col._, columella; _D. M._ depressor mandibulae; _M. B. T. N._, mandibular branch trigeminal nerve; _Sq._, squamosal. KU 64214, ×5.]
[Illustration: FIG. 10. Ventral view of throat musculature in an adult male _Smilisca baudini_ (Superficial musculature on left, deep musculature on right); _A. C._ anterior cornua of hyoid; _Gen. L._, geniohyoideus lateralis; _Gen. M._, geniohyoideus medialis; _Hyo._, hyoglossus; _Omo._, omosternum; _Pet._, petrohyoideus; _S._, submentalis; _Sm._, submaxillaris; _St._, sternohyoideus; _V. S._, vocal sac. KU 64220, × 2.5.]
_Throat Musculature._--The frogs that comprise the genus _Smilisca_ are characterized by paired subgular vocal sacs, essentially the same as those in _Triprion_ (Duellman and Klaas, 1964). The following description is based on _Smilisca baudini_ (Fig. 10).