AUTHOR'S ABSTRACI OF THIS PAPER ISSUED BY THE BIBLIOQRAPHIC SERVICE. MARCH 8 THE DEVELOPMENT OF THE SKULL IN THE SKINK. EUMECES QUINQUELINEATUS L . I . THE CHONDROCRANIUM EDWARD L. RICE Ohio Wesleyan University TWELVE PLATES (THIRTY-THREE FIGURES) CONTENTS 1 . Introduction.......................................................... 120 2 . Material and methods ................................................. 121 3 . Basal plate and associated parts ....................................... 123 1. Basal plate and occipital condyle ................................. 123 2 . Notochord ........................................................ 127 3 . Nerve foramina of basal plate ..................................... 129 4 . Occipital region ....................................................... 135 5 . Otic region ............................................................ 138 1 . General description ............................................... 138 2 . Exterior of auditory capsule ...................................... 139 3 . Interior of auditory capsule ....................................... 142 4 . Foramina of otic region .... ................................... 144 5 . Crista parotica and colume uris ............................... 155 6 . Orbitotemporal region ................................................. 168 1. General description ............................................... 168 2 . Floor of entire orbitotemporal region .............................. 169 3 . Basipterygoid process and associated structures ................... 172 4 . Lateral wall of temporal subregion ................! ............... 175 5 . Fenestrae of temporal subregion .................................. 178 6 . Lateral wall of orbital subregion .................................. 181 7 . Ethmoid region ........................................................ 183 1 . General description ............................................... 183 2 . Nasal septum..................................................... 185 3 . Roof of ethmoid region ......... ............................. 186 4 . Lateral wall of ethmoid reg ............................. 188 5 . Floor of ethmoid region .... ............................. 194 6 . Nerve foramina of ethmoid region ................................. 196 8. Mandibular arch ...................................................... 198 1 . General description ............................................... 198 2 . Dorsal division-palato-pterygo-quadrate cartilage ................ 199 3 . Ventral division--ill eekel's cartilage ............................... 202 119 JOURNAL OF MORPHOLOQY. VOL . 34. NO. 1 120 EDWARD L. RICE 9. Hyoid and branchial arches.. .......................................... 203 10. Summary .............................................................. 206 11. Bibliography .......................................................... 211 12. Description of plates ......... _._. ............ _._. ..................... 217 1. INTRODUCTION Since the publication, in 1900, of Gaupp’s classic paper on the chondrocranium of Lacerta there have been great additions to the accurate and detailed knowledge of the embryology of the vertebrate skull. But the data for comparative study are still inadequate, and many thebretical questions are still dependent for their satisfactory settlement upon the investigation of a more extensive series of species. Especially is it through the investigation of closely related forms that the essential and general can be freed from the inci- dental and individual and built up into a firm foundation for legitimate theorizing. Thus Eumeces has a special claim for consideration because of its comparatively close relationship to Lacerta, which has become the standard for comparison, thanks to the masterly work of Gaupp. The similarities and contrasts of Eumeces and Lacerta may be emphasized most conveniently by a strictly comparative treat- ment based upon Gaupp’s paper (’00). For the most part, both the order of treatment (except for the division of Gaupp’s paper into two parts, descriptive and theoretical, respectively) and the terminology of Gaupp are adopted here. Partial results of this study have been published in the form of brief preliminary notes (’11, ’14); here they appear in more complete form. In the present paper the history is followed only to the stage of maximum development of the chondro- cranium; the fate of the cartilages in later embryos and in the adult skull and the development of the bones, aside from merely incidental references, are left for later treatment. The earlier literature on skull development has been so admi- rably summarized by Gaupp in Hertwig’s ‘Handbuch’ (’05 b) that any further extensive review would be superfluous. CHONDROCRANIUM OF EUMECES 121 The present investigation was commenced under the super- vision of the late Prof. Ernst Gaupp in the Comparative Ana- tomic Laboratory of the University of Freiburg, Prof. Robert Wiedersheim, director. 1 wish at this time to express my hearty appreciation of the courtesies, scientific and personal, which were extended so freely during my stay in Freiburg by Professor Wiedersheim, Professor Gaupp, and the other members of the staff. During the later prosecution of the work I have enjoyed the hospitality of the Lake Laboratory of Ohio State University, the Zoological Laboratory of Harvard University, and the Ma- rine Biological Laboratory at Woods Hole. My thanks are due to Prof. Herbert Osborn, Prof. E. L. Mark, Prof. Frank R. Lillie, and their associates for their many favors. I have also been materially assisted by several of my advanced students in Ohio Wesleyan University, and would especially thank Mr. Joseph I. Taggart, Miss Margaret Cole, and Mr. Clarence L. Turner for the use of models and unpublished work freely placed at my disposal. And, finally, I wish to record my indebtedness to the Ohio Academy of Science for a grant from the Emerson McMillin Research Fund, which has provided technical assistance in the preparation of drawings and in the work of modeling. Through this grant I have been able to avail myself of the services of Miss Mabel L. Hedge, whose artistic and accurate drawings are reproduced in figures 1 to 8, inclusive. 2. MATERIBL AND METHODS The material upon which this paper is based consists of a single brood of eggs collected when the embryos were already consid- erably advanced. They were preserved at intervals during a period of seventeen days. No data can be given as to absolute ages, but the relative ages may be seen from the following tabu- lation. The measurements of the table were secured, after preservation, by means of a thread laid along the embryo. The length of the head is measured from the tip of the snout to the 122 EDWARD L. RICE posterior margin of the tympanum; the body is measured from the posterior margin of the tympanum to the anus. The meas- urements of the tail and of the total length are much less reliable than the other data, owing to the fact that the tip of the tail of almost every embryo was damaged in the preparation of the material. Tabular statement of size and age of embryos studied LENQTH IN MILLIMETERS STAQE AQE IN DAYS Head Body Tail Total 1 X 3.25 6.50 7.00 16.75 2 X+2 3.50 7 .00 7.50 18 .oo 3 x+4 4 .00 8 .DO ? ? 4 x+6 4.50 9.00 ? ? 5 x+9 4.75 9.75 13 50 28 .OO 6 x + 17 6 .OO 13 .OO 20.00 39 00 CHONDROCRANIUM OF EUMECES 123 scales are clearly visible in the epidermis, and the longitudinal stripes of the juvenile color pattern are already conspicuous. Stage 5, which is in nearly the same stage of development as the 31-mm. embryo of Lacerta described by Gaupp, furnishes the foundation for this paper, but earlier and later stages are used freely for comparison. The material was preserved in picro-acetic and stained with Mallory's triple connective-tissue stain (acid fuchsin +aniline blue+orange G)-a stain which leaves nothing to be desired as regards clearness of differentiation of bone and cartilage from one another and from surrounding tissues. The following wax plate models have been available for study and comparison : a. Stage 1. Membranous labyrinth, modeled by Mr. J. I. Taggart. b. Stage 2. Entire skull and first two vertebrae, cartilage only, modeled by Miss Margaret Cole. c. Stage 5. Entire skull and first two vertebrae, cartilage and bone, modeled by the author. d. Stage 5. Cavity of otic capsule, modeled by Mr. J. I. Taggart. e. Stage 5. Membranous labyrinth, modeled by Mr. J. I. Taggart. f. Stage 5. Brain and nerve roots, modeled by Mr. Clarence L. Turner. Figure and brief description published by MY. Turner ('14). g. Stage 6. Posterior portion of skull, cartilage only, with nerve origins, modeled by the author. 3. BASAL PLATE AND ASSOCIATED PARTS 1. Basal plate and occipital condyle The basal plate (figs. 1 and 2), belonging alike to the occipital and otic regions, lends itself to separate and continuous descrip- tion. As in Lacerta, the basal plate consists of a doisally con- cave floor between the otic capsules and extending from the foramen magnum at the posterior to the fenestra hypophyseos at the anterior. The anterior margin is strikingly thickened to form the crista sellaris (fig. 1, crsel.), and from the anterolateral corners arise the trabeculae cranii (fig. 2, trab.), the rudimentary pilae prooticae (fig. I, pi.pr-ot.), and the basipterygoid pro- cesses (fig. 2, pr.b-pt.), which will be described in detail later. 124 EDWARD L. RICE The large fenestra basicranialis posterior (fig. 2, fen.b-c.p.) commences immediately behind