32 



is shown by tlie abdominal testes, the single cloacal outlet, 

 the low cerebral 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 Anteaters 1 . 



The order Bruta is but scantily represented at the present 

 period. One genus, Manis or Pangolin, is common to Asia 

 and Africa ; the Orycteropus is peculiar to South Africa ; the 

 rest of the order, consisting of the genera Myrmecophaga, 

 or true Anteaters, Dasypus or Armadillos, and Bradypus or 

 Sloths, are confined to South America. 



Having defined the orders or subdivisions of the two fore- 

 going subclasses, I may remark that the LYENCEPHALA cannot 

 be regarded as equivalent merely to one of the orders, say 

 Rodentm, of the LISSENCEPHALA, without undervaluing the 

 anatomical characters which are so remarkable and distinct 

 in the marsupial and monotrematous animals. The anato- 

 mical peculiarities of the edentulous LYENCEPHALA^ appear to 

 me to be, at least, of ordinal importance. In these deduc- 

 tions I hold the mean between those who, with Geoffroy 

 St Hilaire, would make a distinct class of the Monotremata, 

 and those who, with Cuvier, would make the Monotremes 

 a mere family of the Edentata. In like manner, whilst I 

 regard the LYENCEPHALA as forming a group of higher rank 

 than an order, I do not consider it as forming an equivalent 

 primary group to that formed by all the placental Mammalia. 



The true value of the LYENCEPHALA is that of one of four 



1 This latter vital character attracted the notice of the earliest observers of 

 these animals. Thus Marcgrave and Piso narrate of the Sloth : 'Cor mo turn 

 suum validissime retiuebat, postquam exemptum erat e corpore per semiho- 

 rium : exempto corde caeteris visceribus multo post se movebat et pedes lente 

 contrahebat sicut dormituriens solet.' BufFon, who quotes the above from the 

 Historia Naturalis Brasilice, p. 322, well remai-ks, ' Par ces rapports, ce quad- 

 rupede se rapproche non seulement de la tortue, dont il a la lenteur, mais en- 

 core des autres reptiles et de tous ceux qui n'ont pas un centre du sentiment 

 unique et bien distinct.' Hist. Naturelle, 4to, Tom. xm. p. 45. 



3 See my article Monotremata, in the Cydop&dia, of Anatomy, part xxvi. 

 1841. 



