SKULL OF A HADROSAURIAN DINOSAUR — GILMORE 491 



has a limited contact with the frontal. The ventral third gradually 

 thins toward the border with an outward inclination of the whole end. 

 The slightly roughened inner surface of this end apparently indicates 

 its lapping union with the missing parasphenoid. At about midlength 

 on the internal side a low longitudinal ridge evidently marks the 

 ventral limit of the olfactory lobes. "Whether these ridges met on 

 the median line, and thus formed the floor of this portion of the brain 

 case, cannot be determined. There is no indication of a median bony 

 septum, such as is present in Tyrannosaurus, and it would appear that 

 in this form the ethmoids enclose an undivided cavity for the olfactory 

 lobes of the brain and form an opening leading into the nasal and 

 prenasal cavities in front of the orbits. In Triceratops ^ the ethmoidal 

 region roofs over the olfactory lobes of the brain, a condition that 

 could not possibly exist in this specimen. 



MEASUREMENTS OF ETHMOID 



Greatest length, anteroposteriorly 24 mm 



Greatest depth, dorsoventrally 44 mm 



SUMMARY 



The study of this disarticulated brain case discloses for the first 

 time in the Hadrosauridae the presence of a distinct ethmoid bone; 

 the presence of a semimovable articulation between the squamosal, 

 supraoccipital, and exoccipital ; and contributes evidence that in this 

 family the supraoccipital is excluded from participation in the 

 boundary of the foramen magnum. 



« Hay, O. P., Proc. U. S. Nat. Mus., vol. 36, p. 102, pi. 2, 1909. 



U. S. SOVERNMENT PIINTINC OFriCI: HIT 



