180 FIELD CoLUMBIAN MusEuMm. 
before mentioned, the diapophyses and ribs are united throughout. 
In 11, 11, and 1v the merging of the three neural arches, and conse- 
quent reduction of space occupied by them in the antero-posterior 
direction, gives to the diapophyses the appearance of radiating from a 
common center. This feature is accentuated by the general tendency 
of sacra to be compressed in this direction while in the matrix, owing 
to the frailty of the arches as compared with the centra. This also 
accounts for the usual convexity of the inferior outline of the sacral 
series which should doubtless be concave. 
MEASUREMENTS. OF SACRUM. 
Lerigth of five‘coalesced .central_ 2-2: + ___ 3 2 ee F360 
Height of sacral + 1-over alls U7 eo 1.350 
Height ofsacral 11 Over allic?22_-0. 2 olu- tigi ee 1.310 
Height of sacral 111 over ‘all---02 2“ Le 1.230 
Height,of sacral 1v ‘over.allis evo se spt a 1.190 
Vertical diameter of centrufm I at anterior end >_.-_ = __ 22 ee .365 
Lateral diametér.of centrum I at anteriorend=_.-2_2- 2-2. 380 
Vertical diameter.of centrum VV at posterior end- ----_8.-__2 
Lateral diameter: of centrum V'at-poStertor,end=: --2.0- 2) fees) ae .360 
Breadth. of.coalesced spines Ii, 115 anddv at crest —.5. =. 2 1390 
Breadth of ‘coalesced Spines#II,‘11l, and 1Vat base 22.520) 220_ ae .285 
Length of spine:above; prezygapophysis:1n 1\.22 0 So a ee sprig dele’ 
Length of spine:above -préezygapophysis ill V -<-~ es ee). .690 
Length of sacricostal. yoke=<- 2-2. - =s0 54.0225 o- Sete et 
MORPHOLOGY OF THE OPISTHOCOELIAN SACRUM. 
The composition of the sacrum in various genera of the Opistho- 
ceelia has been regarded from almost as many points of view as there 
have been writers on the subject. Marsh looked upon the number of 
sacral vertebre as a fixed quantity for each generic group and based 
many of his genera upon this character. In defining the order ‘*Sauro- 
poda’’ he characterized the sacrum as composed of not more than four 
vertebra. In later classifications the number of sacrals-was not given — 
as an ordinal character. Cope placed less stress upon the number of 
sacral vertebre, but used it in generic distinctions. 
Osborn, in 1898, described the sacrum of ‘**‘Camarasaurus’’ as 
follows: **Camarasaurus had five sacral vertebre; three of these con- 
stantly coalesced both by centra and neural spines, two others coalesced 
less constantly and possessed free spines.’’* Soon after, Williston 
offered the following more general characterization: ‘‘It is very clear 
that there are three typical vertebre in all the genera of this family 
(Camarasauride) as well as in the Morosauride, if it be a distinct 
* Bull. Am. Mus., Vol. x; p. 230. 
