59 
The pre- and postzygapophyses, facing in opposite directions, are 
inclined at an angle of about 55 degrees to the horizontal, or about 70 
degrees to each other. Their flat 
articulating surfaces are oval in 
outline, with diameters in the 
proportion of 4 to 7, the shorter 
diameter being transverse. These 
surfaces have about the same 
length as those of the cervical 
vertebra (Figure 30) but are slight- 
ly broader. 
The surface for the attachment 
of the head of the ribs is indicated 
by a roughness of irregular out- 
line occurring toward the front 
of the neural arch at about its 
midheight. 
The size and proportions of the 
anterior vertebra supposed to be 
Figure 31. Anterior dorsal (?fifth) vertebra of fifth Or sixth ^ of the series 
Edmontosaurus, Cat. No. 2289; | natural size, are very similar to the one above 
A, left lateral aspect; B, anterior aspect; C, pos- plpqprihprl onH fio-nrprl • pnnollv 
terior aspect; h, surface for head of rib; nc, neural CieSCriDea ana UgUreU, It IS equally 
canal; ns, neural spine; t, surface for tubercle of Well preserved and any Special 
rib; fp, transverse process; 2, prezygapophysis; 0, reference tO it is not Considered 
postzy gapophy SIS . 
necessary. 
