ilfr. Brookes on a new Genus of the Order Rodentia. 101 



The Rabbit 

 Marmot 

 Urson 

 Agouti 

 Coypus 

 Capromys 



7 lumbar vertebrae. 



7 



6 



6 



6 



6 



Hence it appears, that in the number of the ribs, and of the 

 lumbar vertebrae, the Lagosiomus agrees with the Jerboa, the 

 Squirrel, and the Rabbit. From the former of these its distinc- 

 tions have been already pointed out. From the Squirrel it dif- 

 fers amply in the want of the rotatory motion of the bones of 

 the fore-arm, and in the number of the toes, which in that animal 

 are five upon each foot. In the Rabbit the fibula is anchylosed 

 with the tibia a little below its middle, as in the Jerboa, — a cir- 

 cumstance which takes place also in the Rat. From the Agouti, 

 with which it corresponds in its tridactyle hinder extremities, it 

 is distinguished by the number of the ribs and of the lumbar 

 vertebrae, as well as by various other particulars of the osteology. 

 In the Helamys there are five toes to the fore-feet, and four to 

 the hinder. With the exception of this animal, of the Rabbit, 

 and of the Jerboa, the tibia of Lagostomus exceeds in com- 

 parative length, that of any of the other Mammalia enumerated 

 above. 



One circumstance which has been noticed in the anatomical 

 description is worthy of particular remark ; — the bony union of 

 the radius and ulna in an animal, which, from the testimony of 

 accurate observers, who saw it during its life, employed its an- 

 terior extremities in conveying its food to its mouth. This struc- 

 ture, so far as I am acquainted with the osteology of the Mam- 

 malia, is perfectly unique. It has been hitherto regarded as 

 quite at variance with the existence of claviculae, most of the 



quadrupeds 



