DEVELOPMENT OE THE SKULL IN THE MAMMALIA. 
65 
The end vieiv of the skull (Plate 10, fig. 4), shows the strength of' the wide and 
high occipital arch. The foramen magnum (fan., see also fig. 1) is round above, 
notched below or in front, and it widens out over the condyles. 
The supraoccipital ( s.o .) is roughly semicircular and extends, without an “inter¬ 
parietal ” over it, from the well-arched parietals to the foramen magnum. A hook¬ 
shaped wedge of cartilage still separates it from the exoccipitals (e.o.). The muscular 
impressions in the main piece are well marked ; the outer and lower edge of the bone 
is flanked by the squamosals (■ sq .), and the lowest corner is pierced by a vessel. The ex¬ 
occipitals (e.o.) are roundish, and in this aspect are separated by a considerable band 
of cartilage from the opisthotic bone out of which we see the facial nerve (VII.) pro¬ 
ceeding, and to which the epihyal (e.hy.) has grown. Below, the annuli ( a.ty.) are seen 
in the distance. The proper or anterior condyloid foramen (fig. 1, XII.) must be seen 
from below ; here, the posterior condyloid foramen (p-cf.) is seen outside each condyle. 
An inner view of the ossicula auditus, removed, and freed from the remains of 
Meckel’s cartilage (fig. 6), and an outer view (fig. 7) of those parts attached to the 
capsule, and with the tympanic remnant of the primary bar, show some very instructive 
things. 
The main part of Meckel’s cartilage has been used up—partly ossified and lost in 
the ramus, and partly absorbed. The head of the malleus, the osseous matter of 
which runs forwards as the styliform “ processus gracilis ” ( p.gr .), has, in front of it, 
yet, a large tract of the primary mandible. This thick semiosseous hook (mk.) curves 
itself, after it becomes detached from the rest of the main bar, round the front of the 
tympanic cavity. The distal third is still unossified ; this bony tract is, essentially, a 
second “articulare internum,” such as is seen in the Holostean Ganoids, Lepidosteus 
and Amia; (see Bridge “On the Skull of Amia,” Journ. of Anat. and Bhys., 
Vol. 11, Plate 23), and the writer’s paper “On the Development of the Skull in 
Lepidosteus,” Phil. Trans., 1882. 
But this tract has a greater interest for the morphologist even than this, for such 
a further remnant of the normal mandible is often present in adult Marsupials (see 
Doran, ‘ Ossicula Auditus,’ plate 64), and for a time—during the first autumn—the 
Mole has a similar malleus, as I shall show in my next Part. 
More than that — in a similar malleus of a young Koala ( Phascolarctos cinereus) of 
the same size, nearly, as this young Unau—I find two smallish, but well-defined mem¬ 
brane bones in this premalleal tract; these are seen at once to be the same as the 
“ supra-angulare ” and the “ angulare ” of the Oviparous types. One such bone is seen 
in this case, the angulare (Plate 9, fig. 7, ag.), an oblong splint, pointed at both ends. 
When this temporary mass is removed (fig. 6) then the processus gracilis (p.gr.) is 
seen to be no larger than the manubrium (m.ml.) and parallel with it, but pointed and 
grooved, above, instead of being terete like that process. There is an evident elbow, 
or posterior angular process (p.ag.), to this masked and arrested proximal end of the 
mandible. The lamina uniting the manubrium to the head of the bone is thin and 
MDCCCLXXXV. K 
