. The Quarterly journal of the Geological Society of London . y bounded in the manner above stated, they sometimes shifttheir position backwards and open at the back of the palatines. Insuch cases, however, the palatines are produced towards the middleline, each along its outer edge, into an underlying plate, which roofsover the mouth and forms a floor to the nasal passages. A sectionacross the Plesiosaurian skull might be expected, therefore, to givesome signs of an inflection of the palatine bones, converting theminto incomplete tubes, if such a backward extension of the nasalpassage obtaine
. The Quarterly journal of the Geological Society of London . y bounded in the manner above stated, they sometimes shifttheir position backwards and open at the back of the palatines. Insuch cases, however, the palatines are produced towards the middleline, each along its outer edge, into an underlying plate, which roofsover the mouth and forms a floor to the nasal passages. A sectionacross the Plesiosaurian skull might be expected, therefore, to givesome signs of an inflection of the palatine bones, converting theminto incomplete tubes, if such a backward extension of the nasalpassage obtained in it. INTo such signs, however, are to be detectedin the specimens under consideration. A diagrammatic sketch of afracture passing transversely through is given below (fig. 12) ; itshows plainly the outward and upward bend of the palatines, butnot a trace of an infolding. Fig. 12.—Transverse Section across the Shall of P. megaeephalus,showing the piloted plates flanged upwards and outwards towardsthe Maxillos^ hut not inflected to form a nasal It is a fact too curious to be passed over, however, that theinternal are situated in advance of the external nares of thisPlesiosaur, the anterior margin of the latter being a trifle under2*8 inches behind that of the former. A transverse section through the upper and lower jaws is givenin fig. 13: the upward flange of the palatine is seen meeting themaxilla; and the lower jaw has the usual reptilian composition. 2. Redetermination of the Number and Distribution of the Ver-tebrae and of the Length of the Regions of the Spinal Column.—Ofcervical vertebrae, twenty-nine are visible up to the anterior edgeof the furculum; in all probability one more lies beneath thisbone; and the total number may therefore be taken as consequence of the concealment of a large part of the spinebeneath the pectoral and pelvic girdles, the number of dorsal 476 PROP. W. J. SOLLAS ON PLESIOSATJRTTS Fig. 13.—Transverse Section through
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Keywords: ., bookcentury1800, bookdecade1840, bookidquarte, booksubjectgeology
