196 
MR. W. K. PARKER ON THE STRUCTURE AND 
outside ; tlie hamular processes of tlie pterygoids are small but perfect, and behind and 
outside them the whole of the wide hind skull is flattened, and bevelled, and polished 
to a marvellous degree. On the inside, also, the surface is exquisitely smooth, and the 
bone delicately cellular ; the cochlese have their bony walls polished and thinned down 
so as to show the coils as if through a transparent medium, and the great porch for 
the “ flocculus cerebelli ” is the most remarkable piece of miniature architecture I am 
acquainted with. The bony tubes containing tlie semicircular canals strengthen the 
porch at its margin, and the intervening bone roofing it is extremely thin. The 
base of the skull now shows a shallow but distinct sella turcica, and behind it the 
postpituitary wall is well defined, although rather low. The cribriform plate is very 
large and abundantly perforated. 
But the basal and basilateral regions of the skull, in its floor, although highly 
polished, is marvellously broken up into hills and holes, because of the extreme delicacy 
of the upper table of the bone; the supratympanic bony shell, the cochleae, the 
Jloccular porches, the pituitary cup, and postclinoid wall,—to say nothing of the fora¬ 
mina and fissures for nerves, vessels, and the like,—make this little skull, in its inside, 
a most admirable object for study and contemplation. 
All this is true of the outside or lower surface, but the large flattened tympanic 
annulus, conrpleting the unlipped bony meatus externus, and thoroughly anchylosed to 
the surrounding bones; and the extensive air-galleries that are excavated inside the 
huge basisphenoid, and the small squamosals, may be mentioned. 
The ossicula auditus are figured and will now be described, as they show the last 
specialisation of the inferior arches of the face. 
The malleus (Plate 25, fig. 8, inner , and fig. 9, outer view) shows a very small processus 
gracilis (p.gr.) and a small manubrium [mb.), whose axis forms one continuous curve 
with the body of the bone. In front, under the head, but most on the inside, a consider¬ 
able pneumatic recess is seen, and outside the obtuse angle ( p.clg .) of the manubrium, 
there is a loop-shaped ridge where the remnant of the last tract of cartilage was seen. 
In this malleus almost the whole of the attempted mandibular structures has been 
absorbed; and the Metatherian type, at its loivest grade, has been exchanged for the 
typical Eutherian form. 
The incus has lost much of its typical Mammalian character* (see Plate 28) ; its 
short crus ( s.c.i .) has dwindled to a fine transverse style, the incurvation of the lower 
part of the long crus ( l.c.i .) is almost lost, and the orbicular facet is a mere oblong 
condyloid tract. 
Thus this little representative of the quadratum has lost, not only much of the “otic 
process” (= short crus), but also that special Mammalian character, the orbicular 
plate on an inturned narrow neck, has greatly suffered degradation. Now this relapse is 
* I here include both the Marsupial and Placental Mammals, for in the former the incus has its 
highest development; the long crus and the obricular plate being better developed than in the Eutheria, 
generally. 
