PRESUMABLY THAT OF IGTJANODON MANTELLI. 



745 



rior border is mutilated), this os articulare maybe described as con- 

 sisting of a vertical plate largely appearing in the outer surface of 

 the jaw, and of a horizontal plate projecting inwards from the 

 former in a shelf-like manner, bearing the tympanic articular 

 surface. 



Vertical plate. — The outer surface of this is smooth ; so much of 

 it as lies in advance of the tympanic joint has a roughly quadri- 

 lateral outline (see fig. 1) ; and here its vertical depth is about double 

 that of the part behind it abreast of the tympanic joint, which nar- 

 rows chiefly by the sharp descent of the upper border of the plate. 

 Below, the quadrilateral part is bent inwards, which makes its 

 upper border overhang, particularly above a large foramen to be 

 shortly described. Abreast of the tympanic joint the surface of the 

 plate bends inwards, through the tapering-off of the hinder end of 

 the jaw. 



At the bottom of a shallow circular pit, rather behind and above 

 the middle of the quadrilateral part of this plate, is a large foramen, 

 which would give passage to a cedar drawing-pencil (fig. 1, b). Its 

 inner opening is deeply placed beneath and hidden by a thin lip or 

 sheet rising from the front of the tympanic surface (figs. 1, 2, 3, c). 



Figs. 1-4. — Htght Os articulare o/Iguanodon, one third natural size. 

 Fig. 1. — Outer View. 



a. Tympanic joint, b. Foramen, c. Ascending process from tympanic surface. 

 Fig. 2. — Tympanic Surface, from above. 



\ Ascending process. 



