102 ORIGIN, ETC., OF THE FAUNA. 
FAvUNISTIC DIVISIONS OF CENTRAL AMERICA. 
Central America has been described above as transitional with respect to its 
Mammalian fauna between North and South America. ‘This statement, however, is 
perhaps too general and apt to give a mistaken impression of the actual facts; for the 
transition cannot be described as complete. Its incompleteness, however, is not due 
to the existence of any physical barriers to migration, unless temperature and moisture 
can be described as such. But, as will appear in the sequel, the faunistic do not 
coincide with the political divisions of this land-area. 
The central portion of Mexico forms an extensive plateau rising some 9000 feet 
above the sea, with mountains nearly twice that altitude. This tableland to the north 
is continuous with, and closely resembles in its characters, a great tract of comparatively 
dry territory stretching into North America and embracing the southern parts of 
California, Lower California, Nevada, Arizona, and nearly the whole of Texas. 
Southwards the plateau is continued by the mountain ranges which stretch throughout 
the southern States of Central America In Mexico it rises somewhat abruptly 
from the lower-lying country towards the coast on each side of it; and this country, 
covered for the most part with tropical forest, extends to east and west of the plateau 
up to or almost up to the confines of the United States. ‘Tropical forest-conditions 
also prevail over the greater part of Central America to the south of the plateau, 
although, as has been stated, the country is almost everywhere broken up by 
mountains rising several thousand feet above sea-level. 
It is needless to recapitulate here the facts set forth above regarding the distribution 
of the families and genera of Mammals inhabiting Central America. It is clear, how- 
ever, that those believed to have undergone a long course of evolution in South 
America (Primates, Edentates, Hystricomorphous Rodents, and Marsupials) are wholly, 
or in the main, restricted to the forested tracts above described, although not by any 
means occurring throughout such districts. Most of the genera and families do not 
pass north of Vera Cruz, in Mexico, and Guatemala. Notable exceptions are the 
Armadillo (Dasypus) which reaches Texas, some of the Opossums which occur on the 
Mexican plateau—one, indeed, penetrating far to the north in the United States,—and 
the Porcupine (Erethizon), belonging to the same family as Coendow and ranging 
from Arizona to Alaska. 
Similarly, with the groups which, although known to have been evolved in North 
America or Eurasia, are now dominant in the southern tropical districts of America, 
such as the Tapirs, Peccaries, Brockets (Mazama), most of the Felide, some Procyo- 
nid (Nasua, Potos), and Mustelide (Zayra, Grison). These genera, usually regarded 
as intruders from the south, though the evidence on that head seems inconclusive, are 
mostly restricted to forest-covered tracts of Central America. And the same thing 
applies to the Bats of the families Phyllostomide, Desmodontide, ete. 
