the Skull of DiadomodoiK 



297 



hollows which run along the ridge backwards until they are 

 sudd(Mily terminated by deep fossic. 



The median riiii^e continues backwards until, at a point 

 about halfway to the occi[)ital coiulyles, it suddenly widens 

 and s])lits into two, wliich form the lateral borders of a 

 trian>;nlar area bounded hchiiul by the occipital surface of 

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

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

 by very deep pits. 



^,J. \j 0lk^ 



__ ^ Fet / ■^atsi^' 



PtTar.Foss. Sq. KFar.Foss 



Fig. 1. — Diademodon hroicni, R. 3587. Upper surface, x 1. i 

 digastric groove; Ex.au. M., external auditor}' meatus; t,., 

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

 maxilla ; Na., nasal ; Par., parietal ; Pet., petrosal ; P.Fr., pre- 

 froutal ; Pin., pineal 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. 



