. The Quarterly journal of the Geological Society of London . f these two species are preserved in theBristol Museum; so that I have had a good opportunity of makinga close acquaintance with them, and have succeeded in elucidatingsome points in their anatomy which were hitherto obscure. Plesiosatjrtjs meoacephalus. 1. The Roof of the Mouth.—The skull of this specimen lies on it3dorsal surface, separated from its matrix from the snout to a trans-verse fracture which traverses it across the orbits. The matrixhas been carefully chiselled away from between the rami of thelower jaw, so as to clearl
. The Quarterly journal of the Geological Society of London . f these two species are preserved in theBristol Museum; so that I have had a good opportunity of makinga close acquaintance with them, and have succeeded in elucidatingsome points in their anatomy which were hitherto obscure. Plesiosatjrtjs meoacephalus. 1. The Roof of the Mouth.—The skull of this specimen lies on it3dorsal surface, separated from its matrix from the snout to a trans-verse fracture which traverses it across the orbits. The matrixhas been carefully chiselled away from between the rami of thelower jaw, so as to clearly expose the roof of the mouth and thebase of the skull for its entire length. The anterior part of thebase (fig. 8), which lies in front of the fracture before mentioned, isby a most lucky chance much better-preserved than that behind, andthus affords us an opportunity which has long been desired of ascer-taining more exactly the true nature of this part of the skull. Pig. 8.— Ventral View of the anterior Part of the Skull ofP. megacephalus. (Scale ^.). n, internal naris; /, palatal foramen. It presents, about 2 inches behind the end of the mandibularsymphysis, two oval foramina (fig. 8, n) longer than broad (1*45 inchin length) separated from each other by a bone which extends back- MEGACEPHALUS AND P. BRACIIYCEPIIALUS. 473 wards in the middle line and unites by a splintery suture with thepalatines behind. It shows traces of a straight sutural union along itsmedian antero-posterior diameter, and consists, without doubt, of theconnate vomers. On their outer margin the foramina are bounded(fig. 9) for the anterior three quarters of their extent by the maxillae,for the remaining quarter and along their posterior margin by thepalatines, and along the inner border (as before mentioned) by theconcave outer margin of the conjoined vomers. The vomero-palatine Fig. 9.—Diagram showing the left Internal Naris of P. megacephalus,bounded by the Maxilla, Vomers, and Palatine. (Scale
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Keywords: ., bookcentury1800, bookdecade1840, bookidquarte, booksubjectgeology
