lvon] the hares and their allies 1^7 



the Leporidffi which do not bear ventral spines) possess a median 

 ventral ridge. 



Sacral J'crtcbrcc. — The sacrum in the pikas is entirely different in 

 form from the corresponding structure in the hares and rabbits. It 

 is long and narrow, its greatest breadth being contained in its length 

 about twice. The lateral masses that are attached to the ilia, instead 

 of being expanded into wing-like processes with the greatest width 

 anteriorly, are much less expanded and have nearly parallel sides. 

 The neural spines so distinct and conspicuous on the sacra of the 

 Leporidae are reduced in the Ochotonidae to form a low dorsal ridge, 

 the separate spines having fused with one another. The number 

 of vertebrae entering into the formation of the sacrum of the Ocho- 

 tonidse is four, the same as in the case of the Leporidae. 



Caudal Vcrtchrcc. — The caudal vertebrae in the Ochotonidae are 

 eight in number in all the skeletons at hand except one, which has 

 nine. In three American specimens, Nos. 91,188 and 30,990 from 

 Idaho, and No. 49,620 from Oregon, the first caudal is somewhat 

 narrowed, the next two are slightly wider, with faint indications of 

 lateral projections ; the rest of the series consists of short flattened 

 bodies. The single Asiatic skeleton, No. 49,500, Ochotona lada- 

 ccnsis, central Asia, has mainly the same character of the caudal s, 

 but the individual vertebrae are relatively wider' throughout. 



STERNUM 



LEPORID-Ti 



(Plates XCV, 1-5; XCVI, i, 3-5) 



The sterna of the Leporidae are formed of the usual three portions, 

 presternum or manubrium, mesosternum or gladiolus, and xiphister- 

 num. 



The presternum consists of one piece which is usually longer than 

 any other single segment of the sternum excepting the xiphisternum. 

 It is usually compressed from side to side and marked by a more or 

 less evident ventral keel. At or anterior to its middle the first pair 

 of sternal ribs is attached. 



The mesosternum -consists of four usually distinct segments. A 

 sternal rib is attached at the point of articulation of each segment 

 with the other, as well as at the point of articulation of the prester- 

 num with the mesosternum. At the posterior outer aspect of the 

 last mesosternal segment near the articulation of the xiphisternum 

 two sternal ribs are usually attached. 



