292 ZAGLOSSUS. 
and in Ornithorhynchus forms the narrow bridge across the temporal canal. 
What seems to be an analogous condition is found in certain other groups, 
as in the Cervidae, the Bovidae, and such Carnivora as Mungos (= Herpestes) 
in which the frontal process is largely developed at the posterior end and by 
fusion with the postorbital process makes a complete bony orbit and separates 
the temporal fossa posteriorly. The temporal canal in existing monotremes is 
thus the temporal fossa greatly restricted by the scale-like expansion of the 
posterior part of the jugal. In the Echidna this expansion is divided dorsally 
by a rather deep notch into an anterior and a posterior lobe, the former of which 
overlies the ventral edge of the parietal. In the Proechidna, the notch is much 
less evident, the dorsal outline of the jugal more nearly hemispherical and the 
anterior end extends far enough forward to overlap the posterior corner of 
the frontal. 
Except’ for differences in relative size and form the bones of the palatal 
and rostral regions are essentially similar in the Echidna and the Proechidna. — 
The termination of the palatals is slightly different, however, in the two. In 
the former the medial portion of the palatal is produced posteriorly as a promi- 
nent spine beyond the union with the pterygoid and there is a deep narrow 
reéntrant between the two palatals. In the Proechidna one specimen shows a 
practically similar condition but in five other specimens the reéntrant is broad 
and shallow, and the palatals are rounded or truncated so as to merge with the 
posterior outline of the pterygoids. 
The nasals in the Echidna do not extend posterior to the margin of the 
orbit, whereas in the Proechidna they extend back to a point nearly opposite 
the middle of the orbit. Since they overlap the frontals for nearly a centimeter 
at this point, the latter bones appear for an absolutely shorter distance on the 
dorsal aspect of the skull than in the Echidna. In both, the nasals taper distally 
to a median point at some distance behind the nasal aperture, so that this latter 
is bounded entirely by the premaxillaries which meet and unite dorsally. The 
exclusion of the nasals from forming part of the boundary of the nasal aperture 
is a singular and unique condition to which apparently no attention has hitherto 
been paid. It is probably a specialized development, in part an accompani- 
ment of the elongation of the rostrum. In the Echidna the distance from the 
nasal aperture to the tip of the nasal bones is one fourth of the length of the 
nasals. In the Proechidna it is slightly more than half their length, thus indi- 
cating the relatively greater development of the rostrum in the latter animal. 
In other mammals in which the rostrum is greatly prolonged, for example the 
