130 Field Columbian Museum — Geology, Vol. II. 



column. Von Ammon* thus describes the neck vertebrae of Rhamphor- 

 hynchus longicaudatus : 



" Es sind sieben Halswirbel vorhanden. Atlas and Epistropheus 

 werden hierbei als ein Wirbel gerechnet. Beide miteinander zusam- 

 menhangen, ihre Gliederung und Form sind undeutlich; die Knochen 

 sind durch spathige Masse entstellt. Es folgen nun nach riickwarts fiinf 

 gleichgestaltete, deutlich von einander abgegrenzte Wirbel, dann kommt 

 (der VII in der Reihe) ein von diesen etwas verschieden aussehender, 

 weil anders gestellte Wirbel der den abschluss des Halses bildet; der 

 unter letzterem befindliche Wirbel (der achte, [in reality the ninth]) 

 besitzt bereits eine grossere Rippe, so dass mit ihm die Reihe der Brust- 

 wirbel zu beginnen ist." 



Atlas and axis, PI. XLI, Figs. 3—5. The atlas is coossified with the 

 axis for the most part in the adult specimen, though leaving a distinct 

 sutural line of division in the more immature specimen. In the younger 

 specimen, the coossification is less complete, and the axial intercentrum 

 is also apparent, though indistinguishable in the older specimen. The 

 atlas is composed of the usual number of parts, though the centrum, or 

 odontoid must be small. The intercentrum forms the lower third or 

 more of the cup; it is deeply and smoothly concave, with a sharp cotylar 

 rim, which is nearly semicircular in outline. Its upper border in front 

 has three parts: the middle one, concave in outline, joins the odontoid; 

 the lateral borders, oblique in position, join the bodies of the neura- 

 pophyses. The posterior surface is probably flat, or but slightly concave; 

 the sutural line with the axial intercentrum is nearly parallel to the rim, 

 and the width is slight, though a little greater on the ventral side, where 

 the under border slopes somewhat ventrad toward the axial intercentrum. 



The bodies of the lateral pieces, or neurapophyses, of the atlas com- 

 plete the rim of the cup, each forming a little less than one-third of the 

 circumference. Their lower border unites with the atlantal intercentrum; 

 the inner, lower border, joins the odontoid; while the inner, upper bor- 

 der, thinner and less in extent, unites with its mate in the middle. The 

 dorsal processes or arches are slender, somewhat oblique, and but slightly 

 dilated at the distal extremity, which appears to be free. They apparently 

 curve backward, to be applied throughout the whole of their extent, to 

 the thin neural border of the axis. The bottom of the cup is formed by 

 the odontoid. Its anterior surface has three convex borders of nearly 

 equal extent, ending more acutely above. How deep or thin this bone is 

 cannot be said, and it is not impossible that the surface appearing in the 

 cup is really the anterior face of the body of the axis, the odontoid being 

 obsolete. The inner ends of the lateral pieces are thin, and it is impos- 



*Correspondenzblatt des Naturw. Ver. in Regensburg, 38 Jahrg., 1884, p. 151. 



