DEVELOPMENT OF THE SKULL IN THE MAMMALIA. ig 
is normal; in the Sloths with fewer teeth, and in the toothless Anteaters and Pangolins, 
the stapes is a short columella ; in the lesser Anteater and in the Sloth a slight per- 
foration may take place after ossification, but this element is imperforate in the 
cartilaginous stage. I cannot find that the fore part of Mecker’s cartilage forms 
‘ 
any part of the “ramus,” as Insectivora and other normal Mammals; it seems 
simply to become absorbed, as in the Sauropsida. The angular and coronoid processes 
of the lower jaw are well developed in all except the Pangolins; in them these parts 
are more aborted than in the Echidna. 
Also in the early embryo of the Pangolin the chrondrocranium, instead of equalling 
that of a Frog or a Skate, as it does in most kinds both of this Order and of the 
Mammalia, generally, is very feebly developed, almost as much so as in Serpents and 
Lizards, and, as in the Serpent, the orbitosphenoidal plate, at least its upper part, is 
a separate patch of cartilage. 
In the osseous stage, the Armadillos of the genus Tatusia have their alisphenoid in 
two pieces, like the two separate tracts of the cartilaginous orbitosphenoid of the 
Pangolin, and in this genus, contrary to the rule of the Edentata, but according to 
the rule of the normal Mammalia, the 3rd branch of the 5th nerve notches the hind 
margin of the alisphenoid. 
In the others it primarily notches the outer margin of that free-edged plate, 
although it often becomes enclosed in bone, afterwards, thus, passing, in the adult, 
through a well-formed foramen ovale. Only in the Sloth do [ find a bar of bone 
enclosing the space through which the 2nd branch of the 5th nerve passes out, thus 
forming the foramen rotundum. 
And only in the Sloth do I find the foramen opticum, which begins as a perfect 
passage, surrounded by cartilage behind, converted afterwards into a mere notch, 
thus opening into the sphenoidal fissure. This is primary in Marsupials, and excep- 
tionally so in Sorex vulgaris amongst the Insectivora ; in that type the nerve may or 
may not have a bony bar formed behind it, afterwards. This variation may occur in 
the same individual, the right and left sides differing. But in Marsupials, as in 
the Sauropsida, there is, normally, no postneural cartilaginous bar, either in the 
cartilaginous or the bony stage. 
I shall refer to this imperfect list of modifications of the skull of the Edentata 
in my next and following papers. 
