256 MEMOIRS OF THE CARNEGIE MUSEUM 
Natural History, and we are greatly indebted to him for having kindly allowed us 
the use of this material. It is interesting to know that the chevrons of Cetiosaurus 
vary in form in much the same manner as those of Diplodocus, as has been shown 
by Professor A. Smith Woodward in his paper recently published in the Proceedings 
of the Zodlogical Society of London, 1905, Volume I., p. 239. 
THE STERNAL PLATES. 
Among the puzzling elements of the skeleton of Diplodocus, as well as of other 
dinosaurs which have been discovered, are two bones to which Professor Marsh has 
given the name of ‘“‘sternal plates.” The location of these elements of the skeleton 
has occasioned a great deal of perplexity, and a careful examination of Professor 
Marsh’s writings upon the subject shows very plainly that this distinguished 
authority was by no means certain as to either the location or the function which 
these large sesamoids hold in the skeleton. In his ‘‘ Dinosaurs of North America,” 
Plate XXII., Fig. 1, he represents the sternal plates of Brontosaurus with their 
thickened extremities directed upward and forward, and with their flattened and 
broadly expanded extremities directed downward and backward. On p. 179, Fig. 
30, he represents the corresponding bones of Morosaurus in a reversed position. 
Both Mr. Hatcher and the writer discussed at great length and repeatedly the ques- 
tion as to the proper location of these elements, and finally reached the conclusion 
that the enlarged and thickened extremities of the bones, which manifestly display 
provision for the attachment of large masses of cartilaginous matter, should be 
located so as to point backward, while the thin margins should be directed upward 
and forward, thus making provision for the attachment for the ligamentary 
skeleton of the sternum, no portions of which have been found in a petrified form 
in any specimen which we have discovered, although in one specimen of Bronto- 
saurus, which is described by Professor Marsh, there were found what he terms 
sternal ribs, which, manifestly, were more or less cartilaginous in their structure. 
It appeared to the writer, after a careful consideration of the subject, as altogether 
most probable, that the position which has been assigned these elements in the 
restoration is the correct one. There is no instance of record in all of the paleonto- 
logical researches which have thus far been made, of the discovery of these bones in 
the exact position which they held in the life of the animal. ‘They usually occur 
commingled with the anterior portions of the skeleton whenever this is found 
approximately in sitw. In specimen No. 84 the sternal plates of the Diplodocus lay 
about the middle of the abdominal region, in a position to which they might easily 
have been brought as the bones of the decaying skeleton were shifted about by the 
