458 Miscellaneotis. 



equally developed with the paramastoid in the Teleosauriis, in which 

 the latter process stands out clear of the tympanic : in the Gavial 

 and modern Crocodiles, the paramastoid is much more developed 

 than the paroccipital process, and it also articulates with the tym- 

 panic. In both the Teleosaur and Crocodile, the paroccipital pro- 

 cess is divided from the paramastoid process of the exoccipital by the 

 groove which forms the back wall of the meatus auditorius. 



The basisphenoid presents a moderately extended, smooth and 

 free or non-articular inferior surface, divided by a median ridge : 

 each half of the surface contracts as it rises outwards, and is concave. 

 The posterior angles of the basisphenoid are wedged into the fore 

 part of each hypapophysis of the basioccipital, the rest of the posterior 

 surface of the basisphenoid having a broad sutnral union with the 

 basioccipital. The upper and hinder part of the sides of the basi- 

 sphenoid articulate with the alisphenoids ; below and in front of 

 this articulation is the sutural surface for the pterygoid : the upper 

 surface of the basisphenoid forms the floor of the mesencephalon : 

 its substance is largely excavated by productions of the auditory 

 chamber. 



The alisphenoid contracts a little after it rises from the basisphe- 

 noid, being notched behind for the meatus, and in front for the tri- 

 geminal nerve : it then rapidly expands in antero-posterior extent, 

 but ends about half-way up the temporal fossa, uniting with the 

 parietal above, the orbitosphenoid in front, the mastoid and exocci- 

 pital behind : below it articulates chiefly with the basisphenoid and 

 a little with the pterygoid. 



The parietal is a single, symmetrical, elongate-quadrate bone, con- 

 tracted at the middle, with the angles produced. Posteriorly it forms 

 the upper ridge of the occipital surface, overhanging the super- 

 occipital, and overlapping the inner ends of the mastoids. The 

 upper surface is extensively impressed by the crotaphyte surface : a 

 very narrow longitudinal tract, becoming in old Teleosauri a ridge, 

 divides these surfaces. The lower boundary ofi^ers two wide aud 

 shallow emargiuations, the dividing angle projecting into the suture 

 between the ali- and orbito-sphenoids. The anterior border is notched 

 on each side to receive a process from each frontal. The under sur- 

 face of the parietal contributes a narrow, elongated, shghtly concave 

 tract to the upper wall of the cranium. The parietal rests almost 

 equally on the ali- and orbito-sphenoids. 



The mastoid is a triradiate bone ; its shortest ray descending 

 obliquely outwards and backwards, to terminate the strong ridge for 

 muscular attachments formed chiefly by the exoccipital : the broadest 

 ray extends forwards, forming the hinder half of the upper zygoma : 

 the sharpest and longest ray extends upwards and inwards to form 

 the outer and greater part of the superoccipital ridge, which sharply 

 divides the occipital from the temporal surface. The zygomatic part 

 of the mastoid is sculptured on its outer surface. The mastoid 

 unites with the parietal, alisphenoid, exocci})ital, tympanic, squamosal 

 and poatfrontal : it forms the angles of the back part of the skull, 

 aud knits strongly tcigetber the contiguous bones. 



