158 
MR. W. Iv. PARKER ON THE STRUCTURE AND 
the pituitary. This recess is bounded, behind, by a snag from each tympanic wing. 
These wings are deeply notched in front, on their outer side, and in front of the notch 
the alisphenoid has a strong rib of bone running with its concave outline forwards to 
join the external pterygoid process. This rib is itself notched in the young, but in old 
specimens this notch is converted into a foramen. Here in this immature specimen 
the hole is finished only on the left side— right in the figure. 
The same parts are seen from the hinder aspect of the bone (Plate 20, fig. 8). 
The anterior sphenoid (Plate 21, figs. 7, 8) is less than half the size of the posterior; 
it has coalesced with the compound ethmoidal bone, behind the extensive olfactory fossa 
with the underlying cribriform plate ( cr.p .). The sinuous wings (o.s.) are deeply 
grooved, transversely, near their hind margin; these grooves lead to the optic fora¬ 
mina (II.). These wings are formed by the ossification of only the proximal or 
lower part of the original cartilage (see Plate 17); they lessen, forwards, like the 
large wings, and grow down into a keel on each side before they unite to form the 
short presphenoidal bar. 
This skull is doubly desmognathous, for the vomerine series of bones unite the two 
halves of the nasal labyrinth into one common complex structure (Plate 21, figs. 7-9) ; 
this is very common in the Mammalia; and is sometimes seen in Birds ( e.g ., Gymnorhina 
—the Piping Crow of Australia), where the maxillary palatine floor has an ethmo- 
vomerine floor completed above it. 
The antero-lateral vomers have coalesced with the palatine plates of the premaxil- 
laries, lengthening them considerably ; and the postero-Jateral plates have coalesced 
with the outside of the forks of the main vomer (Plate 21, figs. 7-9), the latter is a 
long thickly carinate bone, bluntly pointed in front. 
That which is most important to remark upon in the ossified nasal labyrinth itself is 
that the various turbinals—nasal, inferior, middle, superior ( n.tb ., i.tb., m.tb., u.tb .) — 
are transformed into a light and porous kind of bone, but when the investing bones— 
nasals, frontals, &c.—are peeled off them the wall is found to have been absorbed ; the 
succeedaneum to this wall is the outer investing plate. Hence, these coils, when 
stripped before they are anchylosed to the investing plates, have large vacuities 
between them, displaying their folds. This is due to the fact that the secondary folds 
or turbinals, ossify first, and only so much of the primary wall becomes ossified as gave 
origin to these out-growths ; the intermediate spaces are absorbed, being pressed upon 
and defended by the superficial bony plates. 
The pre-olfactory region occupied by the inferior or maxillary turbinal (Plate 20, 
figs. 9, 10, front and side views) is very large, and this part is exceedingly complicated, 
as indeed it is in most of the Eutheria; in the Babbit and the Dog, as well as in the 
Hedgehog. 
The lower jaw (Plate 21, figs. 5, 6) is fairly intermediate between that of a Marsupial 
and that of a high Mammal; the three proximal processes are all large and well formed, 
and the lower, or angular, is somewhat inflected as well as thickened. 
