252 MEMOIRS OF THE CARNEGIE MUSEUM 
sacral region and support the ilia are regarded as the sacral bones, then there are but 
ten dorsals. If the anterior vertebra of the five in the sacral region is considered, as 
has been done by Mr. Hatcher and Professor Osborn, a modified dorsal, then there 
are eleven. 
THE SAcRAL VERTEBR&. 
Professor Marsh (“ Dinosaurs of North America,” p. 182) says, “There are four 
vertebree in the sacrum. On Plate XXVIII. he gives a figure of the lower side of 
the sacrum in which he shows but three vertebree. Professor Osborn in his mono- 
graph states, as Professor Marsh stated in his text, that there are four sacral verte- 
bree, and reckons as these four the three figured by Marsh in his plate and the suc- 
ceeding vertebra.’ Mr. Hatcher says: 
“The sacrum in Diplodocus may be regarded as composed either of three, four, 
or five vertebree, according to the individual conception as to which should be con- 
sidered as sacral vertebre. If the sacrals are made to include all those vertebre, 
which, though formerly belonging to the posterior dorsals or anterior caudals, have 
laterally become so modified as to function as sacrals by affording support to the 
ilia, either by bearing true sacral ribs, or by the means of greatly expanded trans- 
verse processes, or by both of these methods, then the sacrum of Diplodocus must 
be considered as composed of five vertebre.” 
The fact is that five of the vertebree are firmly codssified by their centra in this 
region and unite in supporting the ilia. All five perform the functions of sacral 
vertebree. It appears to the writer that probably the most correct view to take of the 
the matter would be to say that the three vertebree intervening between the modified 
dorsal and the modified caudal vertebra are the true sacrals, and to reckon the an- 
terior vertebra with the dorsal series and the posterior vertebra with the caudal 
series. 
THe CaupDAL VERTEBR2. 
Mr. Hatcher accepted Professor Osborn’s interpretation of the sacrals, fixing 
their number at four and including in the sacral series the modified caudal to which 
reference has been made by the writer in the preceding paragraph. Mr. Hatcher 
and Professor Osborn begin the caudal series with the vertebra next succeeding the 
one which functions as a sacral. Professor Osborn estimated the number of caudals 
as thirty-seven. Mr. Hatcher in his Memoir stated that ‘‘ This number will more 
than likely be increased through the addition of a number of rod-like posterior cau- 
dals now known to obtain in the tails of certain other Dinosaurs.” The correctness 
of the prediction made by Mr. Hatcher was strikingly shown by the discoveries 
made in 1901 and 1903. Mr. W. H. Utterback succeeded in 1903 upon the Red 
