40 



BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



The centra are deeply excavated on the sides and inferiorly, this feature "becom- 

 ing more pronounced as the posterior part of the series is approached, where the en- 



A B 



Fig. 23.— Fourth dorsal vertebra of Antrodemus valens Leidy. No. 8367, U.S.N.M. \ nat. size. A, Side view. 

 B, Front view, d, diapophysis; p, parapophysis; z, anterior zygapophysis; z', posterior zygapophysis. 



larged ends are flangelike. The median sides above 

 the middle are pinched in, forming a shallow lon- 

 gitudinal depression as shown in figures 26 and 27. 

 In passing backward in the series these depressions 

 become slightly deeper, though on none except 

 perhaps the last dorsal could they be classed as 

 pits. In both Gorgosaurus and Tyrannosaurus 

 lateral pits are present in most of the dorsal 

 centra. 



The anterior face of the sixth dorsal.is nearly 

 plane, but in the seventh it is slightly concave, 

 this concavity continuing back through the series. 

 The posterior articular surfaces are partly am- 

 phiplatyan, with a characteristic slight anterior 

 concavity in the upper portion of the face below 

 the neural canal. This feature is especially pro- 

 nounced on the last dorsal, where it articulates 

 with the sacrum. The centrum of the twelfth 

 dorsal viewed fro'm the side is slightly wedge- 

 shaped, being narrower below than above — a 

 condition observed in the seventh dorsal of 

 Tyrannosaurus as depicted by Osborn. 1 To a 

 less degree some of the other dorsals are also shorter longitudinally at the bottom 

 than at the top, thus forming a slight upward bow of the articulated vertebral 

 column. The height of the centra exceeds their breadth. 



Fig. 24.— Sixth dorsal vertebra oe Antro- 

 demus valens Leidy. No. 8367, U.S.N.M. 

 i nat. size. Side view. d. diapophysis; p, 

 parapophysis; z, anterior zygapophysis; z', 

 posterior zyga ophysis. 



1 Plate 27, Bull. Amer. Mus. Nat. Hist., vol. 35, 1917. 



