lyon] the hares and their allies 385 



genera. In both Rouicrolagits and Liuinolagus, especially the former, 

 the tibia is more curved than it is in the other rabbits, the inner 

 surface of the lower part of the shaft of the tibia being concave, as 

 it is in Ochotona. 



In most of the skeletons the greatest length of the foot is about 

 equal to the length of the tibia. In Brachylagiis and Sylz'ilagits 

 floridanus siibsp. No. 94,197, from Nevada, the foot is longer than 

 the tibia. In the subgenus Macrotolagus and in the genus Romcro- 

 lagus the foot is shorter than the tibia. 



The tibia and fibula in the Ochotonidae are similar in form to the 

 same bones in Romcrolagns. 



TARSUS 

 (Plate C) 



The tarsal bones in all the skeletons show few differences among 

 the Leporidje, except as to size. The middle cuneiform is not fused 

 to the base of the second metatarsal. 



The tarsus of the Ochotonidse is in general like that of the 

 Leporidse. The middle cuneiform, however, is entirely fused with 

 the base of the second metatarsal. The foot, as a whole, is relatively 

 shorter than it is in the Leporidae. 



In the Ochotonidse there are some small sesamoid bones, on the 

 plantar surface of the tarsus, which are apparently lacking in the 

 feet of the Leporids. These bones are discussed by ]\Iajor at con- 

 siderable length. Their true significance and functions cannot be 

 well determined without the dissection of fresh material. The 

 largest of these sesamoid bones is situated on the plantar surface of 

 the base of the fifth metatarsal. In the Leporidae this bone seems to 

 have become fused with the base of the fifth metatarsal, where it 

 forms a prominent tubercle. 



METATARSUS 



The metatarsals in both the Leporidae and the Ochotonidae are 

 four in number, the first being suppressed. According to their 

 relative lengths the metatarsi in the two families fall into four groups, 

 as follows : The basal width of the metatarsus, measured from the 

 tuberosity of the fifth to an opposite point on the second is contained 

 about three times in the length of the third metatarsal in Lcpiis. It 

 is contained about two and a half times in Sylz'ilagiis, Oryctolagns, 

 Liinuolagns, Brachylagiis, and Pronolagus. It is contained two 

 times in Roiucrolagiis. In Pcntalagus and Ochotona it is contained 

 one and a half times. 



