HATCHER: OSTEOLOGY OF HAPLOCANTHOSAURUS 15 
be valid will doubtless also be found to be provided with five functional sacrals. 
The same remark also applies to the recently described genus Brachiosawrus of 
Riggs. On the other hand it sometimes happens in the skeletons of very old indi- 
viduals that an anterior caudal or posterior dorsal becomes codéssified with the 
functional sacrals. As an example of the latter the sacrum of the type of Bronto- 
saurus excelsus Marsh may be cited. In such instances however there is no danger 
of misinterpreting the additional vertebree since they never bear so-called sacral ribs 
ribs or give any support to the ilia. 
The sacrum in the present genus and species may be described in general as_be- 
ing broad, low, with short neural spines and consisting of five vertebrae with 
subequal, codssified centra. All five of these vertebrae bear parapophyses (sacral 
ribs) and give support to the ilia through the intermedium of these and the dia- 
pophyses. The parapophyses of the three median or true sacrals expand distally 
and unite to form the inner superior border of the acetabulum as is well shown in 
Plate V., Fig. 1. 
Seen from below (Plate V., Fig. 1) the sacral centra appear subequal in length, 
with the transverse diameter of the first and last exceeding that of either of the 
three median or true sacrals. All five of these vertebree bear so-called sacral ribs 
springing directly from the middle of the centra, save that of the first, which springs 
from the superior internal border of the centrum. The excellent state of preserva- 
tion in which this sacrum was found, firmly attached to the ilia of either side, 
demonstrates beyond a doubt the fact that all five of the vertebrae bear those proc- 
esses which have been called sacral ribs. As to whether or not the first of the 
sacrals is homologous with that which in Diplodocus I have described as the last 
dorsal, though there functioning as a sacral, | am as yet undecided. I believe, how- 
ever, that it is, although since it is the neural spines of this and the two succeeding 
vertebree that are codssified in the present sacrum, this fact might be considered by 
some as tending to disprove this assumption, for in Dip/odocus it is the spines of the 
three median vertebree, the true sacrals, that are codssified. However this may be, I 
am inclined to the opinion that the first vertebra which in Diploducus gives support 
to the ilia did in fact bear what has usually been interpreted as a sacral rib and 
should therefore be considered as a sacral by those who accept the presence of this 
element as distinguishing the sacrals. The imperfect condition of all the Diplodocus 
sacra so far discovered precludes the possibility of determining this point with abso- 
lute certainty in that genus. In the type of Diplodocus carnegu the right side of 
this vertebra is present though in a somewhat imperfect condition and presents an 
element which, though occupying a decidedly more elevated position than that of 
