Cranial Osteology of the Hylid Frog, Smilisca Baudini

Part 1

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===================================================================== UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY

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Volume 18, No. 2, pp. 11-35

------------------------- October 15, 1968 --------------------------

Cranial Osteology of the Hylid Frog, Smilisca baudini

LINDA TRUEB

UNIVERSITY OF KANSAS LAWRENCE 1968

UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors of this number: Frank B. Cross, William E. Duellman, Philip S. Humphrey

Volume 18, No. 2, pp. 11-35 Published October 15, 1968

UNIVERSITY OF KANSAS Lawrence, Kansas

PRINTED BY ROBERT R. (BOB) SANDERS, STATE PRINTER TOPEKA, KANSAS 1968 [Union Label] 32-3686

Cranial Osteology of the Hylid Frog, Smilisca baudini

LINDA TRUEB

INTRODUCTION

The paucity of descriptive cranial anatomical work dealing with hylid frogs was pointed out by Trueb (1966) in her paper describing the cranial osteology of Hyla septentrionalis. Comparative studies on the cranial osteology of the genus Smilisca (Duellman and Trueb, 1966), along with other more brief descriptions, reveal variation among cranial characters of hylids. Since these external characters have been useful in defining species, species groups, and genera, it seems worthwhile to pursue correlated studies on internal cranial structure. The following account dealing with the Neotropical tree frog, Smilisca baudini Dumeril and Bibron, 1841, is the first published description of the internal cranial anatomy of a hylid frog, and supplements the recent account (Duellman and Trueb, 1966) of external cranial osteology of the same species. Comparative studies of hylid skulls are expected to yield information of taxonomic importance.

I am grateful to Richard J. Baldauf of Texas A & M University and William E. Duellman of the University of Kansas for critically reading the manuscript and offering helpful suggestions. The findings reported here result from research on Middle American hylids supported by a grant from the National Science Foundation (GB-1441) to William E. Duellman.

Materials and Methods

The serial sections illustrated beyond are from an adult male of Smilisca baudini (KU 89924) having a snout-vent length of 53.0 mm. and a head width (measured at angle of jaws) of 17.0 mm. The specimen was collected 5.2 kilometers east-southeast of Cordoba, Veracruz, Mexico. Transverse sections were cut at thicknesses of 10 and 15 microns on a rotary microtome and stained according to the technique described by Baldauf (1958). Cleared and stained specimens and dried skeletons also were used. Figure 1 is based on KU 68183-4 and Fig. 9 on KU 55614. All other drawings are made from KU 89924. In all cross-sectional figures, bone is represented by solid black, cartilage by stippling, and connective tissue by cross-hatching. Unless otherwise noted all descriptions are given in an anterior-posterior sequence.

Commonly accepted English terms are used. For example, dentary is used in preference to dentale and maxillary process instead of processus maxillaris. If no commonly accepted English term is available for a given structure, the Latin name is retained. For example, the cartilaginous plate separating the cavum principale from the cavum medium is termed the lamina superior.

DESCRIPTION OF INTERNAL CRANIAL OSTEOLOGY

Olfactory Region

Alary cartilage.--The anterior end of the alary cartilage (al. c., Figs. 2-5) lies within the posterior concavity of the alary process (al. proc., Figs. 1-3) of the premaxillary (pmax.). In posterior sections the cartilage assumes a dorsolateral position (Fig. 3), ventral and slightly lateral to the tectum nasi. The alary cartilage remains narrowly separated from the tectum nasi but fuses ventromedially with the septum nasi and forms a nearly complete cartilaginous capsule around the anterior end of the cavum principale. Posterior to the anterior end of the cavum medium and the lamina superior, the alary cartilage separates ventrally from the lamina. In subsequent posterior sections, the cartilage, arcuate in cross section, becomes progressively smaller and terminates at the level of the union of the medial and lateral recesses of the cavum inferior.

Prenasal cartilages.--The superior prenasal cartilage is small; it lies adjacent to the posterodorsal surface of the alary process of the premaxillary, and anterior to the alary cartilage. The inferior prenasal cartilage (inf. pnas. c., Figs. 2-6, and 8) appears posterior to the appearance of the alary cartilage. The anterior terminus lies at the base of the alary process; the cartilage extends dorsally (Fig. 3) along the posterior surface of the alary process and then curves posterodorsally and joins the solum nasi medioventral to the posterior end of the septomaxillary (Fig. 8d).

Tectum nasi.--The anterolateral corner of the tectum nasi (tect. nas., Fig. 2) appears just posterior and dorsomedial to the anterior end of the alary cartilage. The anterior process is short; it fuses medially with the septum nasi forming a complete roof to the cavum principale (Figs. 3 and 4). The oblique cartilage (obl. c.) diverges laterally from the tectum nasi just posterior to the terminus of the alary cartilage (Fig. 6). Medially, the tectum nasi persists, overlaid by the nasal bone laterally.

Septum nasi.--Posterior to the appearance of the septum nasi (sept, nas.) and its union with the tectum nasi (Fig. 3), the septum abruptly expands across the width of the skull medial to the alary cartilage. The septum is entirely cartilaginous posterior to the level of the olfactory eminence, except for a small amount of secondary membranous ossification dorsomedially at a level anterior to the nasal bones. Perichondral ossification commences in the dorsal part of the septum nasi at the level of the olfactory eminence. Endochondral ossification first appears dorsally in the vertical part of the septum at the level of the internal nares. Ossification of dorsal parts of the septum precedes ossification of ventral parts. Perichondral ossification of the ventral part of the septum nasi is first noted at the level of transition between the planum antorbitale and solum nasi. Perichondral ossification gradually gives way to endochondral ossification posteriorly.

Nasal cavities and associated structures.--The cavum principale (cav. prin., Fig. 4) is the most anterior of the nasal cavities. It first appears within the capsule bordered dorsally by the tectum nasi, medially and ventrally by the septum nasi, and laterally by the alary cartilage. The cavity extends posteriorly within recesses of the sphenethmoid to the level at which the septum nasi terminates.

Part 2

The cavum medium (cav. med., Fig. 5) lies ventral and slightly posterior to the anterior end of the cavum principale. It appears slightly anterior to the septomaxillary at the level of the foramen ramus externus narium and ramus medialis narium. The appearance of the cavum medium within the ventrolateral extension of the septum nasi divides the latter into an upper component, the lamina superior (l. sup.) lying between the cavum principale and cavum medium, and a lower part, the lamina inferior (l. inf.) lying ventral to the cavum medium. As the cavum medium increases in width in posterior sections, the lamina superior and lamina inferior lose their lateral connection. The lateral part of the cavum medium diverges in the region of the external nares as the nasolacrimal duct (ncl. dt.) and the cavum medium becomes confluent with the cavum principale (Fig. 6). The posterior end of the cavum medium lies at the level of the posterior terminus of the septomaxillary.

Slightly posterior to the anterior end of the cavum medium the foramen for the ramus externus narium (r. ext. n. f.) and ramus medialis narium (r. med. n. f.) opens ventromedially into the floor of the septum nasi (Fig. 4). The ventral closure of the floor of the foramen completes the solum nasi, marks the anterior end of the recessus medialis of the cavum inferior, and differentiates the roof of the recess, the crista intermedia (cr. int.), from the solum (Fig. 5). The crista intermedia joins the laminae superior and inferior and joins them for a short distance to the septum nasi medially. The anterolateral part of the cavum inferior (cav. inf.) lies ventrolateral to the cavum medium, and extends medially to join the medial recess. The fusion of the two recesses of the cavum inferior completely separates the lamina inferior from the solum nasi (Fig. 6).

Near the level of the union of the recessus lateralis and recessus medialis of the cavum inferior, the crista intermedia separates from the septum nasi, and the lamina superior diverges at its mid-width to accommodate the septomaxillary (spmax.) (Figs. 5 and 6). The lateral remnant of the lamina superior and transition zone between the lamina superior and lamina inferior is short and is quickly replaced by connective tissue. Slightly posterior, the distal edge of the lamina inferior diverges laterally as a small process, which lies dorsal to the pars facialis (p. fac.) of the maxillary. This part of the lamina inferior terminates posteriorly at the level of confluence between the cavum principale and lateral recess of the cavum inferior.

Slightly posterior to the divergence of the crista intermedia from the septum nasi, the crista terminates, thereby separating the lamina superior and the lamina inferior from one another (Figs. 6 and 8). The lamina superior terminates at the level of the infundibulum (inf., Fig. 7), whereas the lamina inferior extends posterolaterally, increases greatly in depth and joins the laterally ascending oblique cartilage (obl. c.) to form the planum terminale (pla. ter., Fig. 10).

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