MR, W. K. PARKER OK THE STRUCTURE AND 
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the inner face of the ramus (cl.) ; but the malleus (ml.) and incus (i.) are now three- 
fourths of them bony; their shape is very similar to that of the other kind (fig. 3), hut 
the head of the malleus (fig. 8, ml.) is heavier, and its handle smaller. A similar 
difference may be seen in the incus (i.). The stapes also (st.) differs in having a larger 
hole, a longer neck, and a larger nucleus of cartilage—the interhyal (or infrastapedial; 
i.hy.) in the tendon of the stapedius muscle. These differences are partly due to 
age and are partly specific .* 
Dissection of the shill of Tatusia hybrida. — Fifth Stage (ripe embryo, 4 inches long). 
My most mature skulls of this type were those of ripe young ; they are all that 
is needful, now, for the interpretation of the highly anchylosed skull of the adult. 
The outer parts of the skull, as seen in a dissection of this specimen (Plate 6, 
figs. 1-4), give a good idea of the peculiarities of the Dasypodian type. The lower 
view (fig. 1) still shows the nostrils and alse nasi (e.n., aim.) on the under surface, but 
the bones have encroached on the cartilage, here. The premaxillaries ( px .) are larger 
and they have, now, a definite palatine tract; they fit, now, well into the notches of 
the maxillaries (mx.). 
The palatine part is not alike on the two sides, being more notched, and hooked on 
the left than on the right. 
These parts do not meet in the middle, but space enough is left to expose the over- 
lying front paired vomers (v'.) The palatine portion of the maxillaries (mx.) only 
forms a narrow tract, gently widening backwards. 
The alveolar region has teeth on all but the front fourth. In front of this tract 
the bone is notched for the premaxillary, and, behind, it bends round the palatine (pa.). 
The flange from the alveolar region is on a higher plane than the submesial part of 
the hard palate ; these two tracts are separated by a perforated sulcus, and the inner 
and higher bony tract is marked by the transverse ridges of the palatal skin. Outside 
these parts the maxillaries spread into large shells of bone, the under and inner part 
of which forms a tunnel for the infraorbital nerve (V 3 .). Behind the short floor of this 
tunnel the whole bone has a notched outline, the rounded concavity of which makes 
the fore and inner border of the imperfect orbit. The jugal process is broad and 
notched for the jugal or malar bone (j.). Inside these parts the penthouse formed by 
the orbital plates of the frontals (f.) can be seen. The rest of the hard palate is about 
half as long as that formed by the maxillaries ; it is mainly made by the palatines (pa.). 
# The remarkable differences just shown between these two closely allied specimens of the sub-genus 
Tatusia (or 9-banded Armadillos) suggest the great importance of careful zoological (Taxonomic) work. 
Forms that to the eye of an observer not well trained in zoological work might easily be mistaken for 
unimportant varieties, may, to the eye of an expert, show very important modifications. Moreover, 
any really important external specific character is almost sure to be correlated with some curious and 
instructive modification of deep-lying structures. 
