MARSH.] 



BIPLODOCUS. 



179 



bone iu Brontosaurus. The short dentigerous portion iu front is de- 

 curved (PI. XXY, fig. 1), and its greatest depth is at the symphysis, as 

 shown in fig. 28 above. The articular, angular, and surangular bones 

 are well developed, but the coronary and splenial appear to be small. 



THE TEETH. 



The dentition of Diplodocus is the weakest seen in any of the known 

 Dinosauria, and strongly suggests the probability that some of the more 

 specialized members of this great group were edentulous. The teeth 

 are entirely confined to the front of the jaws (PI. XXV, fig. 1), and 

 those in use were inserted in such shallow sockets that they were readily 

 detached. Specimens in the Yale museum show that entire series of 

 upper or lower teeth could be separated from the bones supporting 

 them without losing their relative position. In PI. XXVI, fig. 1, a 

 number of these detached teeth are shown. 



29 



30 



Fig. 29. — Sternal plate of Brontosaurus amplus; top view. 

 Fig. 30. — Sternal plate of Morosaurus r/randis Marsh. 



Both figures are one-eighth natural size, a, bottom view; 6, top view ; 6', side view; V, end view; 

 c, face for coracoid ; d, margin nest to median line ; e, inner front margin ; p, posterior end. 



The teeth of Diplodocus are cylindrical in form and quite slender. 

 The crowns are more or less compressed transversely and are covered 

 with thin enamel, irregularly striated. The roots are long and slender 

 and the pulp cavity is continued nearly or quite to the crown. In the 

 type specimen of Diplodocus there are four teeth, the largest of the 

 series, in each premaxillary; nine in each maxillary, and ten in each 

 dentary of the lower jaws. There are no palatine teeth. 



The jaws contain only a single row of teeth in actual use. These 

 are rapidly replaced, as they wear out or are lost, by a series of succes- 

 sional teeth, more numerous than is usual in these reptiles. PL XXVI, 

 fig. 2, represents a transverse section through the maxillary, just behind 

 the fourth tooth. The latter is shown in place, and below it is a series 



