PROFESSOR OWEN ON THE GENUS DINORNIS. 339 



diameter, from the parietal to the basioccipital tuberosity ( i'), is 2 inches 3 lines ; its 

 breadth across the postorbital processes (PI. LIII. fig. 1, 12) is 5 inches. Its length from 

 the paroccipitals (ib. 4) to the fore part formed by the coalesced nasals (ib. is) is 5 inches 



2 lines. 



The flattened end of the nasal process of the premaxillary (ib. fig. 1,22') rests 

 on a shallow elliptical depression of the nasals (ib. is), which are confluent with the 

 fore part of the frontals (ib. 11). This depression is rounded posteriorly, is 1 inch 



3 lines in length and 1 inch in breadth. The rhinal or olfactory fossae (PI. LIV. 

 fig. 1, n, 14') are 2 inches 9 hues in length and 2 inches in breadth, divided by a con- 

 vex transverse projection of the roof (?i') into a larger posterior compartment in) and a 

 smaller and more shallow anterior compartment ( i4' ) ; both are subdivided by a low 

 median ridge, sharpest and most produced in the posterior compartment. At the back 

 and upper part of each lateral division of this compartment arc seen the fine, radiating 

 grooves diverging from the foramina of the cribriform plate (14). 



The tympanic (PI. LIII. 28) is a triradiate bone, with short and strong rays, the 

 lowest being the broadest and thickest. The mastoid condyle (PI. LIV. fig. 2, e) of the 

 tympanic is 1 1 fines in long diameter, 3 fines in the short diameter. The stem con- 

 tracts transversely, expands in the opposite direction, assuming a trihedral shape, 

 widely excavated on the inner facet by the fossa {g), terminating in the large pneu- 

 matic canal. The anterior or orbital process (fc) is subcompressed, obtuse, 7 lines in 

 depth, 10 lines in length ; it is impressed, externally, by an oval facet for the ptery- 

 goid (j)t). The suddenly and largely expanded lower end presents the usual posterior, 

 narrow, oblong concavity (ib. fig. 3, i, h) and the anterior, smaller, but similarly shaped 

 convexity (ib. i) placed at a right angle to the foregoing. On the outer side of the 

 lower end is the usual subcircular, deep depression (PI. LIII. fig. 2, h), for the 

 squamosal element of the zygomatic arch. 



Mandible. — The articular part of the mandible (PI. LIV. fig. 4) is deeply excavated 

 between the articular surfaces (i, i) which are adapted to those so marked on the 

 tympanic (fig. 3). An obtuse angular ridge projects from the inner side of the wall of 

 this concavity ; a pneumatic canal perforates its base. The ramus, extended forward 

 from the articular end, is divided by two longitudinal fissures into three parts, the 

 upper representing the surangular (PI. LIII. fig. 2, 29), the lower the angular (so) ; and 

 the intermediate portion appears to be the back part of a splenial (31). The surangular 

 developes a low convex ridge, with a rough surface external to it, for the insertion of 

 the temporal muscles. Its fore part is excavated externally, to be overlapped by the 

 upper prong of the dentary element (32) : the angular is more extensively excavated, 

 to be overlapped in a similar manner by the lower prong (32") of the dentary: this 

 element had not coalesced with the rest of the mandible, and has been drawn forward 

 to show the articular grooves The dentary curves gently down as it approaches the 

 thick symphysis, where it coalesces with its fellow to form a broad external symphysial 



2 Y 2 



