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HOLLAND: THE OSTEOLOGY OF DIPLODOCUS MARSH 239 
he apparently represented the dentary as forming the superior border of the man- 
dible for a considerable distance behind the last tooth of the lower series, and as 
forming the lower border of the mandible as far as a point a little back of the mid- 
dle of the jaw. A critical examination of the skull (U.S. N. M., No. 2672) made 
by the writer in conference with Messrs. J. W. Gidley and C. W. Gilmore seems to 
show that the surangular extends forward almost to the point where the last teeth 
oceur, and overlaps the dentary, while the dentary extends much further backward 
than is shown in Professor Marsh’s figure. A comparison of Fig. 3 with Professor 
Marsh’s figure reveals the difference in the interpretation given by the writer from 
that given by Professor Marsh in the drawing published by him. 
The Swrangular (Fig. 3 and Plates XXIII. and XXVI.).— The surangular exter- 
nally overlaps the dentary from a point just back of the last tooth and forms the 
upper border of the jaw, extending externally almost to its posterior extremity. For 
about half of its posterior portion it articulates with the angular which is interposed 
between the posterior upper margin of the dentary and the lower posterior margin 
of the surangular. Internally the inner lamina of the surangular, beginning about 
three centimeters back of the symphysis, overlaps the dentary. Along its posterior 
inner surface it was apparently overlapped by the splenial which in the type speci- 
men (U.S. N. M., No. 2672) seems to have been in great part broken away and 
lost, only some fragments of the lower posterior border remaining visible, wedged 
in between the surangular and the anterior internal prolongation of the articular. 
The Angular (Fig. 3 and Plates XXIII. and XXVI.).—In the type specimen 
the angular is externally shown to be wedged in between the posterior margins of 
the dentary and the surangular, and extends backward to the extremity of the jaw. 
Internally it is shown to have had a heavy thickened middle portion lying back of 
the dentary and overlapped by an anterior prolongation of the articular. 
The Articular (Fig. 3 and Plate X XII1.).— The articular forms the articulating 
surfaces of the jaw, overlapping the surangular at the posterior extremity by a well 
developed lateral process, and internally sending forth a long narrow prolongation. 
The Coronoid. —In the specimen No. 2672 (U. 5. N. M.) the coronoid like the 
splenial appears to be missing, the specimen being in this region somewhat 
defective. 
The Tecth (Fig. 3 and Plates XXIII., XXIV., and XXVI.). — Professor Marsh 
pointed out the fact that the dentition of Diplodocus is weak. In all specimens of 
Diplodocus which have been examined there are four teeth in each premaxillary, 
as has already been pointed out. The number of teeth in the maxillaries and the 
dentary varies. In the specimen on which Professor Marsh founded his descrip- 
