OSTEOLOGY OF CARNIVOROUS DINOSAURS. 37 



First and second dorsals (Nos. 10 and 11). — In Antrodemus the point of change 

 from cervical to the dorsal series appears to be distinctly indicated. The features 

 which indicate where this change occurs are; a sudden shortening of the vertebral 

 centra; the transfer of the parapophyses from a low to a higher position on the 

 side of the centrum; a rapid increase in the height of the neural spines; an increase 

 in length of the transverse processes and their elevation to a plane above the hori- 

 zontal; the increased width of the space between the diapophyses and parapophyses 

 and the passing of the opisthocoelus centra to the amphiplatyan type. In Tyranno- 

 saurus Osborn 1 designates these vertebra as " cervico-dorsals, thus considering 

 them transitional in character, which they are to a greater degree than in Antrodemus. 

 The first dorsal of No. 4734, U.S.N.M., lacks the anterior end of the centrum and 

 the upper portion of the right side of the neural arch. The posterior ventral sur- 

 face of the centrum, when compared with the preceding vertebra, is angularly 

 rounded as contrasted with the broad and evenly rounded centrum of the last 

 cervical. Also the median portion of the centrum in the first dorsal is more pinched 

 together. 



The remaining remnant of the right diapophysis indicates that it must have 

 reached a horizontal position whereas those anterior were all deflected below that 

 level. 



The second dorsal (No. 4734, U.S.N.M.) consists of the complete centrum, but 

 lacks most of the neural arch. The anterior end is convex, but much less hemi- 

 spherical than found in the cervical region. The parapophysis is large and its 

 upper edge reaches the neurocentral suture. The median ventral portion is much 

 pinched together transversely forming a decided ventral keel which widens out 

 toward the front. 



Third and fourth dorsals (Nos. 12 and 13). — These vertebrae of No. 8367, 

 U.S.N.M., were found articulated. The centrum is greatly abbreviated as compared 

 with the longer ninth cervical, the third having a slightly cupped posterior face and a 

 nearly flat anterior face. In this individual the third dorsal may be distinguished 

 from all others in the column by the sharp ventral keel on the centrum, which de- 

 velops at its anterior end an expanded triangular face that projects downward below 

 the anterior rim of the centrum and looks forward and downward. The surface of 

 this face stops 23 mm. posterior to the vertical plane of the anterior end of the 

 centrum, from which it is distinctly separated by a shallow transverse groove 

 (fig. 22). The sides of the centrum are moderately compressed, with a small pit that 

 leads into the body of the centrum posterior to the center of the parapophysis. 

 This is the last appearance of these lateral pits, which are found throughout the cer- 

 vical region. In No. 4734 the third dorsal also bears the last pit. 



The pleuropophysis is large, elliptical in outline, the longer diameter being ver- 

 tical, the upper end extending slightly over the side of the pedestal of the neural arch. 

 The neural arch is relatively low and incloses a neural canal of good size. Anterior- 

 posteriorly the arch above its base is considerably shorter than the centrum. The 

 long traverse processes extend outward and upward from the sides of the neural 

 arch, slightly above the horizontal. The articular end presents a roughened, beveled 



i Bull. Amer. Mus. Nat. Hist., vol. 22, 1906, p. 288. 

 144035—20 4 



