228 
MR. W. K. PARKER ON THE STRUCTURE AND 
however, appears to be secondary and not primary as in the Hedgehog. I did not 
see it in the embryo (Plate 32, figs. 4, 5, b.s.), so that tins character is not primary, 
as in the Hedgehog. 
The tympanic wings ( t.h.s. .) are more clearly marked off from the main basal bone 
than in the Hedgehog, and thus a clue is got to their real nature ; they are mere 
periosteal outgrowths, and, bad they arisen independently, their homology with the 
“ ossa bullae ” of the Marsupial would have been seen at once ; they are the 
morphological equivalents of those bones. These tracts are roughly in the shape of 
the shell of a bivalve Mollusk, but they grow inwards ; in front, the right and left 
processes meet. Behind this junction only a small triangular space of the basi- 
sphenoidal botie is seen, it is somewhat apiculated; at the middle, the synchondrosis 
is still present. These shells (or wings) grow outwards and backwards some distance 
beyond their root. 
The alisphenoids are confluent with their common key-stone piece ( al.s., h.s.), they 
are very large, reaching from the fore-third of the tympanic wings (fig. 1) to the 
bottom of the coronal suture (fig. 3). Thus they lie over the large tympanic cavity in 
its front-third ; they also, like their basal piece, have developed a large tympanic 
wing ( t.al.s .) in front of the tympanic cavity ; this wing has converted the hinder 
angular notch (Plate 32, figs. 4, 5 ; and Plate 33, figs. 1, 3) into a foramen—the 
foramen ovale (V 3 .). 
The hole through the alisphenoid, further forwards, is the hinder opening of the 
alisphenoidal canal (al.s.c.) ; the 2nd branch of the trigeminal escapes through the 
sphenoidal fissure. The subdistinct tympanic ake of the basisphenoid, the very large 
alisphenoids, and their tympanic wings, are all characters that are Marsupial, or 
nearly so. 
But the internal carotids do not enter the skull through the basisphenoid ; there is 
no foramen rotunclum; there is a hollow recess under the basisphenoid, and the 
alisphenoids have broken away from the general skull wall, far outside the orbito- 
splienoids. In Marsupials, however, this does not take place, but the planes of these 
alas are coincident, and the alisphenoid, as well as the orbitosphenoid, ossifies 
upwards into the great supero-lateral band of cartilage. 
All these things are intelligible; these low Eutheria are developing typical 
characters, which are curiously mixed up with certain archaic characters inherited 
from the forms on a lower level (Metatheria), from which these Insectivores once 
sprung. 
The auditory capsules are relatively less now than they were in the unripe embryo 
(Plates 32, 33), only the supra-auditory crest—running into the supraoccipital, where 
it is joined by the exoccipital—is still cartilaginous. 
The cochleae (fig. 1, chi.) are well formed, and their position is almost transverse; 
the tegmen tyrnpani is burrowed by the facial nerve (VII.), which emerges 
behind and within the stunted epihyal ( e.hy.); behind the stylomastoid foramen) 
