Slade.] t)() [March 15, 



separate canal for the nerve. The malar ascends to the lachrymal in a 

 flattened plate. In close connection with these conditions the coronoid 

 process of the mandible is small and rudimentary, while the parts around 

 the angle of the ramus are much developed. 



In the Hystricomorpha, the arch is stout. The jugal is not supported 

 by the continuation of the maxillary process, and generally does not ad- 

 vance far forward. The infraorbital vacuity is large and is either trian- 

 gular or oval. The coronary process and the condyle are but slightly 

 elevated above the dental series. 



In the Chinchillidre, the jugal extends forward to the lachrymal. In the 

 Dasyproctidas, Cselogenys is characterized by the extraordinary develop- 

 ment of the jugal arch, which presents an enormous vertical curvature, 

 two-thirds of the anterior portion of which, constituting the maxilla, is 

 hollowed out into a cavity which communicates with the mouth. The 

 nerve passes through a separate canal, adjacent to the infraorbital opening. 



The jugal arch in the suborder Duplicidentata is well developed. 



In the family Leporidse, there are large wing-like postorbital processes, 

 while the jugal, but feebly supported by the maxillary process, continues 

 posteriorly to aid in the formation of the outer side of the glenoid articular 

 surface, passing beneath the process of the squamosal. 



The Lagomyidse have no postorbital processes, and the posterior angle 

 of the jugal is carried backward nearly to the auditory meatus. The infra- 

 orbital opening in the Duplicidentata is of the usual size. The angle of 

 the jaw is rounded, and the coronoid process much produced upwards. 



The Ungulata may at the present time be divided into the Ungulata 

 vera, including the two suborders, Perissodactyla and Artiodactyla, and 

 the Ungulata polydactyla, which comprises the two suborders, Hyracoidea 

 and Proboscidea. 



In its morphology, the jugal arch of the Ungulata presents various 

 modifications. With few exceptions, two bones alone compose it, the 

 squamosal and jugal, which are connected by a suture, the general direc- 

 tion of which is horizontal. Both the horizontal and vertical curvatures 

 of the arch present considerable variations, as does also its relation to the 

 neighboring parts. 



In the Perissodactyla, the family Equidse exhibits an arch, which, 

 although relatively slender, is quite exceptional in its arrangement. The 

 large and lengthened process of the squamosal not only joins the greatly 

 developed postorbital process of the frontal, but passing beyond, forms a 

 portion of the inferior and posterior boundary of the orbit. The malar 

 spreading largely upon the cheek, sends back a nearly horizontal process 

 to join the under surface of the squamosal process above described, while 

 the orbit is entirely surrounded by a conspicuous ring of bone, thereby 

 clearly determining the bounds between it and the temporal fossa, which 

 last is remarkably small. This fossa is bounded above and posteriorly 

 by more or less well-developed crests and ridges. The pterygoids are 

 slender and delicate, without the presence of any fossa. The glenoid 



