1S95.] t)l [Slade. 



surface is much extended transversely, concave from side to side, and 

 bounded posteriorly by a prominent postglenoid process. The angle of 

 the jaw is much expanded. The condyle is well elevated above the 

 molar series, while the coronoid process is long, narrow and slightly re- 

 curved. 



In the Rhinoceridse and Tapiridse, the arch is strongly developed, and 

 composed of the squamosal and jugal processes, which are joined at about 

 its centre by an oblique suture from above downwards, backwards and 

 upwards. In the Tapiridae, the arcli is long, owing to the advanced posi- 

 tion of the orbit. There is a small postorbital process, largest in the tapir, 

 but the orbital and temporal fossae are continuous. The surface for the 

 temporal muscle is extensive. The glenoid fossa presents a transverse 

 convex surface to articulate with the corresponding one of the mandible, 

 which is not much elevated above the dental series. The coronoid process 

 is slender and recurved, while the angle is broad, compressed, somewhat 

 rounded and incurved. 



In the Artiodactyla, the arch is slender and is composed of the process 

 from the jugal, which passes backwards beneatli the corresponding for- 

 ward projecting process of the squamosal, the juncture being by a suture 

 nearly horizontal in direction, and longest in the Cervidse. The jugal 

 sends up a postorbital process to meet the corresponding descending one 

 of the frontal, the suture which unites them being about midway. The 

 bony orbit is thus complete, while the jugal is forked posteriorly. The 

 temporal region is relatively small. The horizontal curvature of the arch 

 is very slight. The glenoid surface is extensive and slightly convex with 

 a well-developed postglenoid process. The pterygoids present a large 

 surface and are situated nearer the middle line than is the case in the 

 Perissodactyla. The condyle is broad and tiat, and the coronoid process 

 is long, compressed, and slightly recurved. The angle is rounded and 

 much expanded. 



The Tylopoda alone among the Ruminantia have large surfaces with 

 crests and ridges for the increased development of the temporal muscle. 

 The horizontal curvature of the arch is greater than in the true rumi- 

 nants, consequently the temporal fossa is wider and deeper — all in correla- 

 tion with the powerful canine teeth. The forked articulation between the 

 molar and squamosal is also more strongly marked. 



Among the non-Ruminantia, the family Suidse exhibit an arch in which 

 the process of the jugal underlying the squamosal extends back to the 

 glenoid fossa — the two bones being connected by a suture, which is ver- 

 tical anteriorly for the depth of half the bone, and then horizontal. The 

 postorbital process does not meet the frontal, in fact all traces of this are 

 lost in Sus scrofa, but in the peccary and Barbaroussa it is quite promi- 

 nent. The arch is short owing to the position of the orbit, and both ver- 

 tical and horizontal curvatures are considerable. The narrow, transverse 

 condylar surface of the mandible, and the small coronoid process with its 



