the Skull of Diademodon. 



297 



hollows which run along the ridge backwards uutil thev are 

 suddenly terminated by deep fossre. 



The median ridge continues backwards until, at a point 

 about halfway to the occipital condyles, it suddenly widens 

 and splits into two, which form the lateral borders of a 

 triangular area bounded behind by the occipital surface of 

 the skull. This area is somewhat depressed on each side of 

 the middle line, and its postero-lateral angles are excavated 

 by very deep pits. 



xAlu^I. 



Sq. Fr. ParFoss 



Fk 



I.— Diademodon brotaii. E. 3587. Upper surface. X 1. Bff., 

 digastric prroove ; Kr.aii.M., external auditory meatus ; /•'/•., 

 frontal; I. Far., interparietal; Ju., jugal; Lac, lachrymal; Mx., 

 maxilla; Xa., na^al ; Por., parietal ; Pef., petrosal ; F.Fi:, pre- 

 frontfil; Pai., piueal foramen : P^., pterygoid; Pt.Par.Foss., pterygo- 

 paroccipital foramen ; Sq., squamosal. 



On each side in this region is a deep fossa opening ante- 

 riorly into the brain-cavity, and passing outwards laterally 

 to terminate at the beginning of the great smooth groove on 

 the root of the zygomatic arch. This fossa is the tympanic 

 cavity. 



