498 TREE PORCUPINES CHAP. 
in both families we have long-tailed and short-tailed forms. 
Cercolabes corresponds to Atherura or Trichys, and Erethizon 
to Hystrix. 
The genus Hrethizon, the “ Urson” of Canada, has a short, 
stumpy tail. Its spines are almost hidden by enveloping hair. 
The fore-feet have four, the hind-feet five toes. The short tail of 
this creature is remarkable when we reflect upon its climbing 
habits. It appears, however, to be a weapon with which it 
strikes sideways at the enemy. 
Of the Neotropical genus Cercolabes (sometimes called Sphin- 
gurus, Synetheres, or Coendow) there are some eight or nine 
species, all found in Central and South America. The animal is 
Fig, 244.—Brazilian Tree Porcupine. Sphingurus prehensilis. x3. 
arboreal, and has in correspondence with that habit a prehensile 
tail. The spines are not so stout as in the Ground Poreupines, 
and are often coloured yellowish or reddish. in correlation with 
its tree-frequenting habits the bones of Cercolabes show certain 
differences from those of the Ground Poreupines. The scapula is 
broader and rounder in front than is that of Hystrix; the 
phalanges of the thumb (which is rudimentary) are fused 
together as in the Canadian Zrethizon ; but those of the very 
small hallux are also fused, whereas in Hrethizon, as in Hystriz, 
they are separate. In one species, C. insidiosus, Sir W. Flower 
states that there are as many as seventeen dorsal vertebrae 
and thirty-six caudals. The tail is thus very long. In C. 
villosus there are fifteen dorsals and twenty-seven caudals; eight 
ribs reach the sternum, which is composed of seven pieces, the 
