OSTEOLOGY OF CAENIVOKOUS DINOSAUKS. 



39 



surface on the ventral side for articulation with the tuberculum of the rib. They are 

 supported from beneath by converging laminae arising from the front and back 

 pedicles which unite to form a single vertical plate that supports the diapophysis at 

 the central line throughout its entire length. A deep cavity extends inward beneath 

 and back of the prezygapophysis, greatly lightening the bone but without materially 

 decreasing its strength. 



The anterior zj'gapophj^ses project but slightly beyond the face of the centrum. 

 They look upward and inward; are of large size with 

 the greatest diameter transverse. The neural spine is 

 relatively short, wide behind, with a deeply concave 

 surface, narrow in front, with broad convex surface. The 

 median part of both front and back presents rough rugose 

 surfaces. Between the postzygapophyscs at the base of 

 the spine a pit extends forward and downward into the 

 arch above the neural canal. 



The articular surfaces of the posterior zygapophyses 

 are nearly horizontal, with a slight pitch downward to- 

 ward the front. Their posterior borders are within the 

 posterior face of the centrum. 



The fourth dorsal (tig. 23) vertebra differs from the 

 preceding by the development of a slightly heavier, 

 transverse and spinous processes; more elevated position 

 of the capitular facets on the sides of the neural arch; 

 the distal end of the centrum less deeply cupped, with an- 

 terior extremity plain; great increase in the overhang of 

 the prez3'gapophyses. The absence of a lateral pit, and 

 apparently the last appearance of the two converging 

 lamina giving support to the transverse processes. In 

 the succeeding dorsals a single plate arises from the posterior pedicle, the anterior 

 one having disappeared. The last appearance of the pinched in sides which makes 

 the lower median portion keel-like. 



Fifth dorsal (No. 14.). — The fifth dorsal vertebra appears to be missing in 

 No. -8367, U.S.N.M., but the centrum lacking most of the neural arch is present in 

 No. 4734, U.S.N.M. In so far as it can be compared it differs from the precechng 

 vertebra by the deeper excavation of the sides and bottom, thus making the ends 

 appear more flangelike, and by the higher position of the parapophysis. 

 • Sixtfi to the thirteenth dorsal (Nos. 15 to 23.). — Though found disarticulated, as 

 shown in figure 21, these vertebrae are thought to represent a continuous series; 

 and since they differ so little from one another, can be best described collectively. 

 In size they increase gradually from front to back. 



Fig. 22.— Third dorsal vertebra of 

 Antrodemus valens Leidy. No. 

 8367, U.S.N.M. i XAT. SIZE. Side 

 yiE'W. d, Di.APOPHYsis; p, parapo- 

 physis; Z, ANTERIOR ZYGAPOPHYSIS; 

 Z', POSTERIOR ZYGAPOPHYSIS. 



RIB, No. 11, L; 44. Head of thoracic kib, No. 9, L; 45. Thoracic rib. No. io, L; 46. Head or thoracic rib, No. 8, L; 

 47. Fragment; 48. Process to seventh dorsal vertebra; 49. Capitulum to rib; 50. Thoracic rib, No. 5, R; 51. Capitu- 

 LUM to kib, No. 2, L; 52. Axis and portion of atlas. (See fig. 18 ax.); 53. Third cer\ical vertebra. (See fig. 

 18, 3.); 54. Fourth cervical vertebra. (See fig. IS, 4.); 55. Fifth cervical vertebra. (See fig. 18, 5.); 56. Cervi- 

 cal rib, of axis, left side; 57. Ninth cervical vertebra. (See fig. IS, 9.); 58. Thoracic rib, No. 2, L; 59. Two 

 (axis right side) cervical ribs, one tooth; 60. Thoracic rib. 



