lyon] the hares and their allies 365 



6. Lcpiis, having a total of thirteen to fifteen caudals, of which the 

 first only is of the first form, the next five to seven, usually seven, of 

 the second form, and the remaining five to seven of the third form. 



7. Oryctolagiis, with a total of sixteen to seventeen caudals, of 

 which the first is of the first form, the next six or eight of the second, 

 and about the remaining eight or nine of the third form. 



OcnOTONID^ 



The vertebral column of the Ochotonidse presents nearly as many 

 and as marked differences from that of the Leporidse as do the 

 skulls of the former from those of the latter. 



Cervical Vcrfcbrcc (pi. xcii, i). — The cervical vertebrae of 

 the Ochotonida? have the same general characteristics as in the 

 Leporidse. They are decidedly shortened antero-posteriorly, the 

 laminae of the posterior ones being very narrow. This shortening in- 

 volves the axis but not the atlas. The latter has the free extremity 

 of the transverse processes moderately expanded. The costo-trans- 

 verse processes of the third, fourth, and fifth cervicals are placed 

 more obliquely to the axis of the vertebral column than the same 

 processes are in the Leporidse. In the sixth they become horizontal 

 as they do in the hares. The transverse process of the seventh 

 cervical differs from that in the Leporidas in not being pierced by 

 a costo-transverse or vertebral foramen. 



Tlwrocic Vcrtcbrcr. — The thoracic vertebrae of the Ochotonidse are 

 entirely different from the same series of vertebrae in the Leporidse, 

 they are 17 in number instead of 12, the thoraco-lumbar vertebrae in 

 the two groups being 22 and 19 respectively. The first 12 of the 

 thoracic vertebras in the Ochotonidse are exactly homologous with 

 the 12 thoracic vertebrae of the Leporidae. The arrangement of the 

 facets for the heads and the tubercles of the ribs is entirely similar. 

 The five remaining rib-bearing vertebrae of the Ochotonidse are 

 practically indistinguishable from one another as well as from the 

 twelfth, except by the slightly greater size of each succeeding 

 vertebra. 



The spinous processes are relatively shorter in the Ochotonidae, 

 and this is especially true in the posterior thoracic region from the 

 twelfth onward where the spines are all low and slightly inclined 

 forward. Each neural spine of these posterior thoracic vertebrae 

 arises by a broad base from the whole length of the neural arch ; the 

 free extremity of the process is nearl}' as long as the base, the 

 posterior edge being slightly concave. 



