268 
MR. W. K. PARKER ON THE STRUCTURE AND 
most unmistakably Marsupial; the sudden ascent, so to speak, above the general level 
in these types has been partial, and combined with a failure to free themselves 
from low and archaic characters derived from an ancestry belonging to an inferior 
grade. 
As to the relative size of the brain this is evidently one of the highest of the 
Insectivora; it may be said in this to approximate at once to the Lemurs and 
the lower Carnivora. To the Lemurs it is comparable also in possessing a large and 
well developed orbital ring, rare in low forms, keeping its own special character 
in having a huge oval fenestra in the jugal arch, where the squamosal overlaps the 
jugal bone. 
The hard palate is less complete than in Galeopithecus, but more perfect than 
is normal for an Insectivore. The external pterygoid approaches that of the adult 
Petrodroinus, where there is a large oblique lamina of bone outside the proper ptery¬ 
goid. But in the embryo of the closely allied Rhynchocyon, at this part there is 
manifestly a shell-like tympanic wing to the alisphenoid, as in Marsupials. Here in 
Tupaia there is a hole through the root of the external pterygoid process; this is 
evidently the counterpart of the alisphenoidal canal of certain Insectivora, Carni¬ 
vora, &c. ; in size, that process equals what we have in Marsupials. The supra¬ 
orbital foramen is very large, and is further forwards than in Galeopithecus; in Pteropus 
it is still further back. 
But the annulus tympanicus and os bullm are not only well developed, they are 
also the almost perfect counterparts of what we find in the lesser Australian Marsupials, 
especially Petaurus sciureus; the greater degree of anchylosis, which has completely 
fused these two elements of the ear-drum, is the only difference I can find in the two 
types. The lower jaw is a good intermedium between that of a Marsupial and that 
of a normal Eutherian. 
Summary and Conclusion. 
Although this paper is confessedly only a fraction of what is necessary to be done 
in this polymorphic Order, it at least shows how difficult a group it is to handle. 
For the Insectivora are set in the midst of the other Mammalia—low and high ; 
they might be called the Biological stepping-stones from the Metatheria to the 
Eutheria. 
One thing can be done, even now, with the present fragmentary knowledge of the 
structure and development of the Insectivorous types—we can assure ourselves that 
these types are immediately above the Marsupials; that they have the Bats 
(Chiroptera) obliquely above them; that their nearest relations must be sought for 
amongst extinct Eocene forms; and that lowly as they are—arrested and often 
dwarfed to the uttermost, so that Nature could not safely go further in that direction, 
