LYOn] the hares and IHEIR ALLIES 345 



ZYGOMATIC ARCH 



The zygomatic arch of the Leporidse is well developed. Seen 

 from above or below it is very narrow, and is much flattened when 

 seen from the side. In the adult but two bones seem to make it up, 

 viz., the zygomatic process from the squamosal, and what is appar- 

 ently a very long backwardly projecting zygomatic process of the 

 maxilla, but this latter consists of the true malar or jugal bone, 

 which forms most of the zygoma and fuses at a very early age with 

 a small zygomatic process of the maxilla. The zygomatic process 

 of the squamosal is a triangular foot-like structure attached to the 

 squamosal by a narrow pedicle. The squamoso-zygomatic suture 

 remains distinct throvighout old age. The malar projects caudad 

 of the zygomatic process of the squamosal, to a greater or less 

 extent. In the family Leporidse the antero-inferior angle of the 

 zygoma is usually enlarged and flares outward to a greater or less 

 extent. 



The heaviest zygomata are seen in Roincrolagus and Limnolagus, 

 in each of which it is thick and deep, especially deep in Romcrolagus. 

 In Lepus and Brachylagns the zygoma is deep but not thickened. 

 In Oryctolagns the anterior half of the zygoma is deep, but in the 

 posterior half it is shallower. Sylvilagus and Pronolagus have 

 zygomata that are rather thin and shallow when compared with the 

 zygomata of the other genera. 



The foot-like extremity of the zygomatic process of the squamosal 

 is shorter in Lepus than it is in most of the other Leporidse. The 

 external lateral length of the squamoso-malar suture is contained 

 about two times in the superior border of the malar, measured from 

 the anterior end of the squamoso-malar suture to the antero-inferior 

 angle of the orbit. In Oryctolagus Pentalagus, and Caprolagus, 

 on the other hand, the foot-like extremity of the zygomatic process 

 of the squamosal is considerably enlarged, so that the lateral length 

 of the squamoso-malar suture is contained between one and one and a 

 half times in the superior border of the malar, measured from the 

 anterior end of the squamoso-malar suture to the antero-inferior 

 angle of the orbit. In Romerolagus the foot-like extremity of the 

 zygomatic process of- the squamosal is moderately enlarged ; in 

 Brachylagns it is relatively slightly larger than it is in Lepus. In 

 Sylvilagus and Pronolagus the size of the foot-like extremity of the 

 zygomatic process of the squamosal has about the same relation to 

 the rest of the zygoma that it has in Lepus. In Limnolagus, the 

 foot-like extremity of the zygomatic process of the squamosal is 

 short. 



