186 Prof. Owen on the Class Mammalia. 
twenty pairs—of ribs, forming a very long dorsal, with a short 
lumbar, region of the spine in the Two-toed Sloth, recalls a lacer- 
tine structure. The same tendency to an inferior type is shown 
by the abdominal testes, the single cloacal outlet, the low cere- 
bral development, the absence of medullary canals in the long 
bones in the Sloths, and by the great tenacity of life and long- 
enduring irritability of the muscular fibre, in both the Sloths and 
Ant-eaters.* 
The order Bruta is’ but scantily represented at the present 
period. One genus Manis or Pangolin, is common to Asia an 
Africa; the Orycteropus is peculiar to South Africa; the rest of 
the order, consisting of the genera Myrmecophaga, or true Ant 
eaters, Dasypus or Armadillos, and Bradypus or Sloths, are con- 
fined to South America. 
monotrematous animals. The anatomical peculiarities of the 
edentulous Lyencephalat appear to me to be, at least, of ordinal 
importance. In these deductions I hold the mean between those 
who, with Geoffroy St. Hilaire, would make of the Monotremaia 
a distinct class of animals, or with De Blainville, a distinct sub- 
class (Ornithodelphes) of Mammals,} and those who, with Cuvier, 
house) as forming a group of higher rank than an order, I do 
. 
classes of the Mammalia; that its true equivalency is with the 
Li ions are to be found 
* This latter vital character attracted the notice of the earliest observers of one 
us 
"2 , 0) 
Brasilix, P 322, well remarks, “Par ces rapports, ce quadrupéde se rapproche Di 
+ See m article onotremata, in the Cyclopedia of Anatomy, part xxvi, 1841, 
raphie, fascicule premier, 4to, 1839, p. 47. 
Nat, of Mammalia, part i, 1845, p. 18. 
