AND AFriNITIES OF POTAMOGAIE. 



11 



narrow, forming by their union a very convex margin posteriorly, which is received 

 between the parietals and a deep notch anteriorly, which receives the nasal bones. 

 The frontals are entirely excluded from the orbits by the anterior extension of the 

 parietals, which, passing between them and the lachrymals, are separated from the 

 maxillaries by a very narrow extension of the lachrymals, which ascends to unite with 

 the frontal. The frontal suture is obliterated posteriorly, but anteriorly it continues as 

 an harmonia. The nasal bones are long and flat, forming a very convex edge posteriorly, 

 where they are received between the frontals, while then- anterior free edge presents a 

 wide semicircular notch. The nasal suture, except for a short distance posteriorly, is 

 entirely obliterated; the external edges of the single bone, thus formed, are nearly 

 straight and parallel. 



The zygomatic process of the squamosal forms a small, horizontal, triangular plate, 

 whose lower side affords a surface for the glenoid cavity. This cavity is bounded behind 

 by a broad vertical process, which checks the retraction of the mandible ; the axis of 

 the cavity is inwards and slightly forwards. 



The facial plate of the maxillary is united internally with the premaxillary, the 

 nasal, and the frontal, anteriorly with the premaxillary, and j,- g 



posteriorly with the lachrymal. The alveolar margin for the 

 hindmost four teeth projects outwards and backwards, form- 

 ing, by its coalescence with the rudimental malar, a com- 

 pressed, sharp-edged process. There is no zygomatic arch. 

 The antorbital foramen is very large. The orbits ai'e very 

 badly defined ; they are marked by no postorbital process, 

 and are continued mthout interruption into the wide tem- 

 poral fossa. 



The palatine plates of the maxillary form the greater por- 

 tion of the palate ; the palatines form the posterior third, and 

 the premaxillaries about a sixth. Two large incisive notches 

 exist in the premaxillary, and are completed into foramina 

 by the anterior edge of the palatine plate of the maxillary. 



The pterygoid ridges converge from before backwards, 

 and enclose a deep, narrow interpterygoid fossa, whose roof 

 is continued without interruption into the inferior surface 

 of the basisphenoid and basiocciptal. 



The horizontal ramus of the mandible is straight, with its upper and lower edge 

 parallel ; it forms with its fellow an acute angle, with a rather long and very oblique 

 symphysis. The condyle is borne on a distinct neck ; its axis is directed inwards and 

 slightly do\ATiwards and forwards. The posterior margin of the ascending ramus is thin, 

 and runs from the neck of the condyle upwards and slightly forwards to the coronoid 

 process, and downwards and backwards to the prominent hook-like angle. The anterior 



c2 



Lower jaw, twice the nat. size. 



