HATCHER: OSTEOLOGY OF HAPLOCANTHOSAURUS 17 
Should we ever be so fortunate as to discover representatives of the very earliest 
Sauropod Dinosaurs it is not at all improbable that in these the sacrum will be 
found to consist of only these three vertebree. This number is, however, a decided 
advance over that which is supposed to have constituted the sacrum in the primitive 
reptilia. This supposition, however, is at present purely conjectural though sup- 
ported by considerable evidence. If we consider the three median vertebree as the 
true sacrals the anterior might very appropriately be called a dorso-sacral and the 
posterior a sacro-caudal. 
In all the functional sacrals the parapophyses spring from the anterior extremi- 
ties of the centra of the several vertebrae, but in the first and second frwe sacrals 
there is in each instance some slight union between the posterior extremities of the 
centra of these vertebree and the succeeding parapophysis as shown in Plate V., Fig. 1. 
Viewed from above, the diapophyses of the sacrals in Haplocanthosawrus are each 
seen to be formed by the union of two lamine. One of these springs from the 
spine of that vertebra to which the process pertains and the other from the antero- 
external margin of the spine of the immediately posterior sacral. These lamin 
rapidly converge both inferiorly and exteriorly and unite in forming the diapophy- 
ses or transverse processes. These are on a level with the superior border of the 
ilium and a short distance before coming in contact with that element they expand 
anteroposteriorly and present broad, rugose, superior surfaces. 
The neural spines of all the sacrals are extremely short as compared with the 
same elements in either Diplodocus or Brontosawrus and in this respect they more 
nearly resemble the same elements in Morosawrus. Those of the three posterior 
sacrals are directed upward and a little backward. ‘The spines of the three anterior 
sacrals are coalesced and form an elongated bony plate. In Diplodocus and Bronto- 
saurus itis the three (sometimes the two anterior in the former genus) true median 
sacrals that have the spines coalesced. Superiorly and posteriorly the spines are 
much expanded and they each present prominent lateral rugosities at the apex. 
Seen from behind or in front the sacrum is considerably distorted by pressure. 
In the drawings, Plate V., this distortion has been for the most part eliminated and 
the sacrum appears low and very broad with the neural arches of only moderate 
height when compared with those of the dorsals. In so far as I have been able to 
determine there is in the present genus no unusual development of the neural canal 
in the region of the sacrum. 
The principal characters of the sacrum in the present genus are well shown in Plates 
IV. and V., where in the former comparative views are given of the pelves of Bron- 
tosaurus, Diplodocus and Haplocanthosawrus with their respective sacra in position. 
