the Skull of DiiiJemodon. 303 



by its freely open sides. Anteriorly to the pituitary fossa 

 the basis cranii is continued by a very thin deep plate (now 

 pierced in the specimen by an artificial hole) which is visible 

 tor about 1 cm. 



The long u[)wardly directed processes are either exaggerated 

 posteiior clinoid processes — an interpretation which is 

 supported by a specin en of Cynoynatlius described later on 

 — or they are homologous with tlie processi anteriorcs infc- 

 j'iores of the pro-otics of Spheiiodon. 



Outside the foramen for the nervus facialis the periotic 

 l)ears a strong process which articulates by a suture with the 

 posterior ramus of the pterygoid ; tliis process has a notch 

 anteriorly and interiorly and another posteriorly and exter- 

 nally : the anterior of these notches is not completed into a 

 foramen^ but the posterior forms, with the paroccipital 

 process, the pterygoid^ and a small process of the squamosal, 

 a comparatively large oval foramen, the pterygo-paroccipital 

 foramen (fig. 3). 



liising from this pterygoid process of the periotic is a 

 plate of bone which nnites above with the parietal and is 

 provided with a thin lamina which covers the groove already 

 described lying at or near the junction of these two bones. 

 Posteriorly this bone passes directly into the anterior face of 

 the paroccipital process, which is somewhat excavated, so as 

 to form a wide groove leading i'rom the pterygo-paroccipital 

 foramen to tlie post-temporal fossa. This groove is roofed 

 in front by a thin process which arises from the outer face 

 of the periotic and passes backwards and outwards as a 

 continuation of the covering of the parieto-periotic groove 

 to meet a similar process of the squamosal. 



The anterior border of this pro-otic part of the periotic 

 has a sutural union with the posterior border of the upper 

 part of the columella cranii, from which it is separated lower 

 down by a foramen ; this foramen, the posterior border of 

 which is formed by a notch, the incisura pro-oticum of the 

 periotic, must have transmitted one or more branches of the 

 V. nerve; its posterior border is smooth, and leads into a 

 groove which passes backwards and outwards to tlie ptervgo- 

 paroccipital foramen ; this groove is roofed by a thin lamina 

 from the periotic, which joins with that which covers the 

 groove between the pterygo-paroccipital foramen and the 

 post-temporal fossa (fig. 5). 



The whole of this system of laminae covering grooves is 

 perfectly preserved on the right side of the skull, but has 

 been destroyed on the left side, so that the grooves them- 

 selves are visible. 



