4 
61 
comparison with the anterior dorsals the neural arch is lower, the neural 
spine longer, thicker, and not so broad antero-posteriorly. 
The articulating surfaces of the zygapophyses are larger than in the 
anterior dorsals, the difference being principally in the breadth. Their 
outline is broadly oval, the proportion of breadth to length being about 
as 4 to 5. They slope at an angle of about 26 degrees to the horizontal 
and are farther apart than those of the anterior dorsals. The anterior 
border of the neural spine starts narrowly from between the prezyga- 
pophyses and is continued thinly upward to about the midheight of the spine. 
From each postzj-gapophysis a short, stout flange proceeds upward to 
the neural spine as lateral boundaries to a median excavation which 
becoming shallower in its upward course channels the posterior border 
of the neural spine to above its midlength. 
The transverse processes are shorter than, and slender in comparison 
with, those of the anterior dorsals, and lack the latter’s conspicuous develop- 
ment of flanges. They proceed directly outward from between the 
pre- and postzygapophyses with only a slight inclination upward. Their 
strongest connexion below is with the anterior border of the neural arch 
in the nature of a buttress merging with the prezygapophyses. The 
outline of their cross-section at midlength is somewhat oval with the 
greater diameter horizontal, more rounded in front than behind, and more 
than twice as broad as deep. 
Measurements of Posterior Dorsal Vertebra of Paratype of Edmontosaurus. 
Mm. 
Maximum height 498 
Maximum breadth (distance between outer ends of transverse processes), about ... 317 
Length of centrum 75 
Breadth of same 184 
Height of same 182 
Amount of concavity of posterior end of same 25 
Height of neural spine above base of transverse process 220 
Antero-posterior breadth of same at midheight 74 
Thickness of same at midheight 21 
Height of neural canal 41 
RIBS. 
The ribs of Edmontosaurus at present available for description belong 
to the paratype and consist of the pair in place on the cervical vertebra 
above described (Figure 30), the pair preserved with the posterior dorsal 
also already described (Figure 32), and two, presumably a pair, apparently 
belonging to the anterior dorsal vertebra shown in Figure 31. 
Cervical Ribs. The ribs of the cervical vertebra. Figure 30, are 
double-headed and very short, and consist mainly of a triangular plate 
of bone, diminishing backward, composed of the shaft and the broad 
tubercle set in a vertical plane. The neck is given off below from the 
front of and at right angles to the shaft, its junction with the shaft being 
sharply angulated externally. The neck is broad antero-posteriorly, 
and thin, thickening internally for the formation of the head. This 
latter, connecting with the short parapophysis, is much broader antero- 
posteriorly, than deep. The posterior portion of the shaft is short, slender, 
and triangular in cross-section, being flat above, and keeled below by 
the backward continuation of the angulation at the outer termination of 
the neck. 
8329—5 
