246 TEETIAET VEETEBEATA OF THE EATtTM. 



of the exoccipital is separated from the ventral portion which joins the basioccipital 

 by a rounded notch, which seems to have formed the hinder border of the foramen 

 lacerum posterius. Close to the inner angle of this notch the body of the bone is 

 perforated by the condylar foramen, the inner opening of which is on the inner face 

 of the base of the condyle. 



The sujaraoccipital (soc.) forms the whole of the upper part of the occipital surface : 

 it is gently concave from side to side, and in the middle line bears a vertical ridge 

 which increases in height towards the upper border, but stops short before reaching it. 

 This bone, together with the parietal, forms the upper part of the extraordinarily 

 developed lambdoidal crest, the two bones sometimes uniting in a suture as much 

 as 5 cm. deep. The lateral portion of the crest for a short distance is formed by the 

 supraoccipital alone, which here extends on the side of the skull, forming part of 

 the posterior end of the temporal fossae. Beneath this the bone j.oins the squamosals 

 and by its ventral border the exoccipitals. 



The basioccipital (boc.) is a very broad bone, probably forming the ventral angles 

 of the occipital condyles. Its dorsal (cranial) surface is convex from side to side, the 

 ventral concave. In front near its point of union with the basisphenoid the bone 

 widens out and bears' on its outer angles a pair of large roughened tuberosities 

 which project outwards and downwards. 



The basisphenoid is a very broad flat bone, uniting with the basioccipital behind 

 in a long straight transverse suture. Laterally the boundaries of the bone are obscure ; 

 probably it united with the lower end of the alisphenoid, but if so the suture is 

 completely obliterated : behind this it unites in a complicated suture with the 

 squamosal just internal to the inner end of the articular surface for the mandible. 

 In front the bone is overlapped on either side by the posterior ends of the pterygoid, 

 which runs back to about the level of the glenoid surface. 



The parietals (pa.) form the roof of the strongly compressed cranial portion of the 

 skull. Posteriorly they unite with the supraoccipital in a very deep suture, forming 

 the upper part of the lambdoidal crest : in the middle line they join one another also 

 in a very deep suture to form the high sagittal crest. The cranial region, though 

 very narrow, is somewhat more inflated than in Z. osiris, and beneath the sagittal 

 crest is gently convex from above downwards. Ventrally these bones unite with the 

 portion of the supraoccipital which appears on the hinder wall of the temporal fossa, 

 and in front of this with the squamosal in a suture running downwards and forwards ; 

 the antero-ventral angle of the parietals forms a blunt projection apparently for muscle- 

 attachment. The union with the frontals occurs about 3 cm. behind the great 

 supraorbital expansions of those bones ; the suture is a complex one, but, speaking 

 generally, it runs first downwards, then downwards and backwards. In this region both 

 the parietals and frontals are enormously thickened. 



The frontals (fr.), as just mentioned, unite in a complex suture with the parietals, 



