4 6 
MR. W. K. PARKER OK THE STRUCTURE AND 
yet segmented from it, thickens downwards, then comes the shorter ceratohyal (c.hy.) 
not ossified, and the hypohyal ( h.hy .) the same. The body (b.li.br.) has no retral 
process, and is unossified at present; the thyrohyals ( t.hy .) are partly ossified, and 
are in this type segmented off from the body. 
In these things Dasypus shows itself more as a normal Mammal, whilst Tcitusia is 
very low and abnornal. 
Bradypodida:. 
This second and only other group of Neotropical Edentata with imperfect teeth is in 
as great a contrast with the first as can be well imagined, and yet I quite agree with 
Professor Flower in looking upon all the Edentata from that region, toothed or 
toothless, as being suckers from one common root-stock (see Proc. Zool. Soc., 1882, 
pp. 358-367 ; and Art. “ Mammalia,” Encyc. Brit., 9th edit., vol. 15, p. 384). I shall 
describe the South American forms first, and then take up the Palseotropical kinds ; 
in both the extreme diversity of the existing forms, and in some cases their almost 
extinct condition—-just one or two species of an extremely isolated type—suggest, 
powerfully, the great losses this group has suffered since its evolution. 
If any one doubts that the short-faced Sloths are intrinsically of the same stock as 
the long-faced Anteaters of the same region, I would refer him to my figures and 
descriptions of the scapula in these curiously dissimilar forms (‘Shoulder-girdle and 
Sternum,’ Plates 2 L—23, pp. 199-207). 
My materials for working out the skull in this group were as follows :— 
First Stage. Embryo of Unau ( Cholopus didactylus ),* 3^ inches long (Plate 1, 
figs. 1, 2.) 
Second Stage, Embryo of Ai ( Brodypus ) ( Arctopithecus)^ -? sp.) 5 inches long. 
Third Stage. Young of Unau ( Cholopus Iloffmanni), 8 inches long. 
Fourth Stage. Young, half-grown, of Ai (Bradypus tridactylus, Linn.). 
I have just given reasons for supposing that the Tatous ( Tcitusia ) are less typical 
than the species of the genus Dasypus, so I shall now give reasons for considering the 
Bradypodidae, generally, as inferior to the Dasypodidse, as a whole, Cuvier’s insight 
was never better shown than when he classed the heterogeneous Edentata together— 
both the Old and New World forms ; and the same instinct, which led him to put the 
Monotremes with them, was not so far out as seems at first sight. I am satisfied that 
the Edentata in becoming “ Eutheria ” never utilized the Metatherian stage, but 
passed rapidly—at a bound, so to speak—from the Prototherian stage, into the basal 
region of the highest group. There, however, they have stayed; they are just equi¬ 
valent, in their fullest development, to the lowest and most generalized of the In- 
sectivora, some of which, very probably, are modified and improved “ Metatheria,” or 
Marsupials. 
* This Embryo has seven cervical vertebras; G. Iloffmanni has only six. 
