46 MR. W. K. PARKER ON THE STRUCTURE AND 
yet seomented from it, thickens downwards, then comes the shorter ceratohyal (c.hy.) 
not ossified, and the hypohyal (h.hy.) the same. The body (b.4.b7r.) has no retral 
process, and is unossified at present; the thyrohyals (¢.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 Tatusia is 
very low and abnornal, 
BRADYPODID. 
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 FrowEr 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. 858-367 ; and Art. “ Mammalia,” Encye. Brit., 9th edit., vol. 15, p. 384). I shall 
describe the South American forms first, and then take up the Palzeotropical 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 21-23, pp. 199-207). 
My materials for working out the skull in this group were as follows :— 
First Stage. Embryo of Unau (Cholopus didactylus),* 34 inches long (Plate 1, 
figs. 1, 2.) 
Second Stage. Embryo of Ai (Bradypus) (Arctopithecus),( 
Third Stage. Young of Unau (Cholopus Hoffmannz), 8 inches long. 
Fourth Stage. Young, half-grown, of Ai (Bradypus tridactylus, Linn.). 
? sp.) 5 inches long. 
I have just given reasons for supposing that the Tatous (Zutusia) are less typical 
than the species of the genus Dasypus, so I shall now give reasons for considering the 
Bradypodidie, generally, as inferior to the Dasypodidee, as a whole. Cuvirr’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 vertebra ; C. Hoffmanni has only siz. 
