3^0 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



Each of the second and third lumbar vertebrse has a prominent 

 ventral spine, the hypophysis. A smaller hypophysis is found in 

 the first lumbar, and on the twelfth thoracic and the fourth lumbar 

 vertebrse the hypophysis is usually indicated by a low ventral ridge 

 on the centrum. 



The zygopophyses are prominent in the lumbar vertebra, and the 

 articulating surfaces are directed laterally instead of horizontally 

 as is the case with the cervical and thoracic series of vertebrje. 



The last lumbar vertebra is peculiar in being shorter than any 

 of the others and in having shorter and more slender transverse 

 processes. 



The lumbar vertebrse of the Leporidas possess several well-marked 

 variations, constant for certain groups and making good characters 

 by which to determine them. The most important variations occur 

 in the length, shape, and attachment of the transverse processes, and 

 they may be outlined as follows : 



1. Large rabbits having wide and long transverse processes with 

 the free extremity expanded. The length of the longest process 

 equals the length of the centrum to which it is attached and half 

 the length of the centrum in front. The attached portion of the 

 transverse process rises abruptly from the anterior half of the 

 side of the centrum. All the members of the genus Lepns have the 

 transverse processes of the lumbar vertebras of this form. 



2. Medium sized rabbits having the lumbar transverse processes 

 of the same relative length and width as in the above group. In- 

 stead, however, of arising abruptly from the anterior half of the 

 lateral aspect of the centrum, each process has a rather long posterior 

 root coming from nearly the whole of the posterior half of the 

 centrum, sharply sloping into the process itself. The skeletons 

 having such transverse processes on the lumbar vertebrae belong to 

 the genera Sylvilagns and Oryctolagiis. 



3. Medium-sized rabbits wuth the transverse processes slightly 

 shorter than they are in the two preceding groups, the longest 

 process equaling the length of the centrum to which it is attached 

 and a fourth of the centrum in front. The processes are much 

 broader than they are in the former groups, so that they appear much 

 shorter than they really are. The free extremities are more expanded 

 than they are in any of the genera except Ronicrolagus. The 

 attached bases are very wide, coming from the whole side of the 

 centrum, and the angle between the main axis of the transverse 

 process and the side of the centrum is filled in with thin bone 

 especially marked in the anterior part of the lumbar series, approach- 



