LOXOLOPHODON AND UINTATHERIUM. 



25 



affording, as remarked above, an admirable opportunity for the study of the bones 

 and foramina of the base. The condyles projecting downwards and slightly back- 

 wards are raised upon a short neck. This is perforated by the condylar foramen. 

 Just above the upper level of the condyles and perforating the rim of the 

 occipital crest is the stylo-mastoid foramen. Immediately in front of the con- 

 dyles, bounded anteriorly by the post-glenoid process and externally by the peri- 

 otic mass, is a deep space. Into this projects the paroccipital process, which 

 does not extend below the level of the basi-occipitals. Marking the postero- 

 internal angle of this space is the foramen-lacerum posterius. On the antero- 

 internal side is the foramen-lacerum medius, and just external to this is the 

 upward-directed external auditory meatus. This has a wide open entrance 

 behind the post-glenoid process, and narrows quickly as it enters the skull. 

 The low paroccipital process is immediately behind this. 



A deep groove leads forwards on the inner side of the post-glenoid pro- 

 cess, terminating in the foramen ovale. Immediately in front and internal to this 

 is the posterior opening of the short alisphenoid canal. This canal pierces the 

 base of the pterygoids ; it is one of the characters common to all the Dino- 

 cerata, and distinguishing the sub-order from the Pantodonta. It transmits the 

 external carotid artery for part of its course. It is one of the characters which 

 the Dinocerata possess in common with the Proboscidia and Perrissodactyla. 



If the sutures and foramina have been correctly interpreted, the Alisphenoids 

 extend well around on the inner side of the glenoid fossa, forming a short sutural 

 connection with the basi-occipitals. The limits of the Presphenoids cannot be posi- 

 tively determined ; they are very narrow forwards. The lower portions of the 

 pterygoids are wanting in all our specimens. According to Cope, they form a 

 high backward continuation of the posterior nares. 



The Exoccipitals, if the suture has been discovered, are found to extend about 

 an inch forwards in front of the condyles. Here is an obscurely marked suture 

 showing their junction with the mastoid portion of the periotic. This is about 

 an inch and a half broad, with a considerable upward extension on the side of 

 the head. Here it is perforated by the stylo-mastoid foramen, which is placed 

 high. This surface is extremely rough for muscular attachments. The basi- 

 occipitals narrow rapidly forwards and, terminating opposite the post-glenoid 

 processes, are convex from side to side ; they form a narrow suture with the basi- 

 sphenoids, which are obscurely marked off from the presphenoids. 



