lvon] the hares and their allies 433 



The first lower premolar much resembles the anterior half of the 

 first lower premolar of Lcpiis. It has two reentrant angles on the 

 external face and one on the internal. 



The second, third, and fourth mandibular cheek teeth of Ochotona 

 are quite like the corresponding teeth of the Leporidae, but the divis- 

 ion into anterior and posterior portions is more marked and the two 

 portions are entirely subeciual. 



The last lower molar is small, irregularly oval in outline, its 

 pointed end being toward the external side. A posterior portion to 

 this tooth is completely lacking. 



Vertebral Column. — The cervical vertebra (pi. xcii, i) of the 

 Ochotonidse 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 involves the 

 axis but not the atlas. The latter has the free extremities of the 

 transverse processes moderately expanded. The costo-transverse 

 process of the third, fourth, and fifth cervicals are placed more 

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

 in the Leporidae. In the sixth they become horizontal as they do 

 in the hares. The transverse process of the seventh cervical differs 

 from the same process on the same vertebra in the Leporidae in not 

 being pierced by a costo-transverse or vertebral foramen. 



The thoracic vertebrae of the Ochotonidae are seventeen in number. 

 The first twelve of the thoracic vertebrae, in Ochotona, are exactly 

 homologous with the twelve thoracic vertebrae of the Leporidfe. The 

 arrangement of the facets for the heads and the tubercles of the ribs 

 is entirely similar. The five remaining rib-bearing vertebrae of 

 Ochotona are practically indistinguishable from one another, as well 

 as from the twelfth, except by the slightly greater size of each suc- 

 ceeding vertebra. 



The spinous processes are relatively shorter in Ochotona, and this 

 is especially true in the posterior thoracic region from the twelfth 

 onward, wdiere 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 ex- 

 tremity of the process is nearly as broad as the base, the posterior 

 edge being slightly concave. 



That part of the transverse process of the thoracic vertebra which 

 articulates with the tubercle of the rib is of the same form in the 

 two families. Associated with this transverse process in Ochotona 

 are the metapophysis and the anapophysis. Both of these processes 

 are first seen on the third thoracic as mere tubercles. The anapo- 



