Transverse sections through otic capsule
Fig.20. Transverse sections through otic capsule:a) level of anterior ledge of otic capsule;b) anterior level of pars interna plectri and pars ascendens plectri;c) level of pars media plectri;d-f) successive levels of operculum and pars media plectri;g-h) posterior levels of operculum. Abbreviations:corn. prin., cornu principalis;cr. par., crista parotica;op., operculum;p. asc. pl., pars ascendens plectri;p. ext. pl., pars externa plectri;p. int. pl., pars interna plectri;p. med. pl., pars media plectri;sq., squamosal;tymp. r., tympanic ring;vl. l. ot. c., ventrolateral ledge of otic capsule.
Ossification in otic and occipital regions.—The otic region of the cranium is largely unossified. At the level of the optic foramen (Fig. 14) the floor of the neurocranium is cartilaginous but completely underlaid by the bony parasphenoid. The taenia tecti marginales and the tectum synoticum are covered dorsally and laterally by the frontoparietals. Perichondral ossification representing the prootic bone occurs at the margin of the optic foramen and somewhat posteriorly over part of the floor of the neurocranium. Perichondral and endochondral ossification occurs in the sides of the neurocranium ventral to the lamina perpendicularis. This ossification expands laterally until it meets the crista parotica dorsolaterally and forms the dorsal part of the prootic bone. The anteroventral edge of the otic capsule remains cartilaginous. Posteriorly, at the level of the anterior acoustic foramen, endochondral ossification is meager and restricted to the dorsomedial parts of the otic capsule, plus a small amount in the neurocranial floor; perichondral ossification is restricted to the peripheral areas showing endochondral ossification. Posteriorly, endochondral ossification is restricted in the dorsal part of the otic capsule but somewhat increased in the floor of the capsule. The lateral part of the otic capsule posterior to the terminus of the operculum and the ventromedial and dorsomedial parts of the neurocranium remain unossified.
Articular Region
In the anterior sections (at the level of the oculomotor foramen) the angulosplenial (angspl.) is a moderate-sized bone (Fig. 15). Meckel's cartilage (Mc. c.) is present as a small ovoid cartilage lying dorsolateral to the angulosplenial. Posteriorly, Meckel's cartilage is dorsal to the angulosplenial. The cartilage increases in size at the level of the posterior acoustic foramen, and the angulosplenial decreases in size posteriorly. At the level of the posterior border of the posterior acoustic foramen, the maxillary terminates and is replaced by the quadratojugal. The quadratojugal, ventral arm of the squamosal, pterygoid process, pterygoid, and Meckel's cartilage converge. At the level of the jugular foramen (jug. f.) (Fig. 19) the quadratojugal is incorporated into the squamosal-pterygoid process-pterygoid complex. The complex is narrowly separated by connective tissue from Meckel's cartilage ventrally. The quadrate process (quad. proc.) is represented by the cartilage bordered dorsally by the pterygoid process and the ventral arm of the squamosal, and ventrally by Meckel's cartilage. At the posterior terminus of the skull all bony elements of the articular region terminate, except for a small terminal part of the angulosplenial underlying Meckel's cartilage.
SUMMARY
Since no accounts comparable to the preceding forSmilisca baudiniare available for other hylid frogs, it is meaningless to attempt any discussion dealing with character significance or variation within the Hylidae. There is considerable literature treating bufonids, leptodactylids, ranids, and various Old World genera (see Baldauf, 1955, for a review of these works). Likewise, a comparison at the familial level based on the study of a single species seems inadequate and premature. By way of summary and synoptic description a list of cranial osteological characters ofSmilisca baudiniis presented. The items selected enable comparison with similar compilations by other workers, and are based in part on my unpublished observations of other hylids.
1. Compared to hylids not having integumentary-cranial co-ossification, the dermal roofing bones ofSmilisca baudiniare extensive, and the skull is well-ossified internally. In contrast to most casque-headed hylids (those having integumentary-cranial co-ossification), the dermal roofing bones are much less extensive, the dermal sphenethmoid (see Trueb, 1966, p. 563) is absent, and internal ossification is less extensive.
2. The solum nasi is not ossified; the septum nasi is ossified only posteriorly, and the olfactory eminence is supported by the cartilaginous solum nasi and the bony prevomer.
3. The lingual process is absent. There is no palatal cartilage isolated between the premaxillaries.
4. The anterior end of the cavum medium lies anterior to the cavum inferius.
5. The septomaxillary is basically a U-shaped structure and has a dorsal, anteriorly curved, ramus on the lateral branch and a longitudinal loop of bone ventrally.
6. A distinct pars nasalis is absent on the maxillary.
7. A cartilaginous sclera is present.
8. The taenia tecta marginalis and the tectum synoticum are the only roofing cartilages present.
9. The external part of the plectral apparatus (columella) is directed anterolaterally. The pars ascendens plectri is fused with the crista parotica.
10. The pseudobasal process is fused to the otic capsule.
11. The cornu principalis of the hyale fuses with the pseudobasal process.
12. Two acoustic foramina are present.
13. The sphenethmoid and prootic are synchondrotically united.
14. The frontoparietal is separate from the prootic and exoccipital.
15. The prootic and exoccipital are fused.
16. A bursa angularis oris is present.
LITERATURE CITED
Baldauf, R. J.
1955. Contributions to the cranial morphology ofBufo w. woodhouseiGirard. Texas Jour. Sci., 7(3):275-311.
1958. A procedure for the staining and sectioning of the heads of adult anurans. Texas Jour. Sci., 10(4):448-451.
Duellman, W. E.
and
L. Trueb
1966. Neotropical hylid frogs, genus Smilisca. Univ. Kansas Publ., Mus. Nat. Hist., 17:281-375, pls. 1-12.
Trueb, L.
1966. Morphology and development of the skull of the frogHyla septentrionalis. Copeia, 3:562-573.
Transmitted April 18, 1968.
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