A New Rabbit from Mexico. 



171 



Animals differing so widely in habits and manner of progres- 

 sion as the present species and the ordinary rabbits would be 

 expected to differ in their skeletons. Fortunately, Mr. Nelson 

 preserved a perfect skeleton of the new rabbit, which on com- 

 parison with those of the several subgenera of Lepus shows differ- 

 ences of considerable morphologic weight. 



The clavicle is complete and articulates directly with the 

 sternum (fig. 33) — a thing that never happens in the genus 

 Lepus. Huxley describes the clavicle of the rabl)it as "incom- 

 plete at both ends," and Flower states that it " is very short and 

 is suspended by long ligaments between the scapula and the 

 sternum." The manubrium or presternum is broadly exi)anded 

 between and anterior to the 

 articulation of the first pair 

 of ribs (fig. 33), a condition 

 unknown in the genus Lepus, 

 in which it is always long 

 and narrow (fig. 34). Flower 

 calls attention to the corre- 

 lation existing between the 

 form of the presternum and 

 the degree of development of 

 the clavicle, stating that " the 

 presternum is compressed 

 and produced forwards in 

 those rodents in which the 

 clavicle is absent or rudimen- 

 tary," as the hares, and '' is generally broad in the forms which 

 have the clavicle well developed, as the rats, beavers, &c." This 

 interesting correlation is well exemplified in the Popocatepetl 

 rabbit, which, having a complete clavicle, has also a broad manu- 

 brium. The segments of the mesosternum (between the pre- 

 sternum and xiphoid) are only three in number (fig 33), while 

 in all the subgenera of Lepus the number is four (fig. 34). The 

 ribs are correspondingly reduced, only six pairs instead of seven 

 articulating with the sternum. The tubercles of the ribs are not 

 produced into spiniform processes, as in Lepus, And disa})pear in 

 the sixth pair. In Lepus they extend to the eighth pair. The 

 scapula is rather narrow, with a long metacromial process, as in 

 Lepus. There are four sacral vertebrae, as in Lepus (the first and 

 anterior part of the second articulating with the ilia), and nine 



Fig. 33— Sternum of 



Romerolagiis nel- 

 soni (nat. size). 



Fig. 34— Sternum of 

 Lepus timidtis (much 

 reduced). 



