DEVELOPMENT OF THE SKULL IN THE MAMMAILIA. 251 
orbital foramen is seen near the front of this bony selvedge. The postorbital processes 
seem to clasp the parietals behind; these, the largest of the series, carry on and 
increase the general, gentle convexity of the skull-roof; the frontals wedge into them 
before, and the interparietal (7.p.) behind, so that the sagittal suture is scarcely more 
than two-thirds of the length of the frontal. The fore edge of the interparietal (7.p.) 
makes the lambdoidal suture bracket-shaped; that transverse, oblongo-oval bone, 
raises a new convexity over the hind brain; at present, the parietals are scarcely 
imprinted at all by the top of the temporal muscle. 
This skull, which reminds one of anything rather than that of an Insectivore—for the 
Colugo might be called a small primordial Herbivore, with a parachute—has pneumatic 
squamosals as in the Marsupials ; the squamous suture is seen in this upper view, and 
also the swelling of the bone caused by large air-cells outside the temporal fossa, The 
short zygomatic process is also seen in this view, and the thick top edge and hollow 
inner face of the jugal or malar (j.) which reaches far back, as we shall see in the other 
figures. Another thing is seen here in this marvellous little Herbivore, namely, the great 
backward extension of the maxillaries (mz.), with their large dentary region (see also 
figs. Land 3). We see also, obliquely over the growing hind sockets, the hinder opening 
of the infraorbital foramen or channel for the 2nd branch of the 5th nerve (V*.). 
Outside that passage, in the antero-external part of the orbit, there is another large 
passage, this is the lachrymal canal in the lachrymal bone (Lc., 1), a large perforated 
shell of bone growing out upon the face, as well as forming a large part of the orbital 
cup in front. 
All these things want supplementing by the lateral, lower, and end views of the 
skull (figs. 1 and 3; and Plate 38, fig. 1). 
The side view (Plate 38, fig. 1) shows that the face is deflected considerably 
an 
and that there is a definite hollow between the nasal and frontal 
embryonic character 
regions above. 
The orbital and temporal regions run into each other, but the enclosure of the post- 
orbital region is begun. 
In the adult (Plate 39, fig. 3) the cranial cavity and the upper nasal region, from 
the end of the snout to the crista galli are equal; now (Plate 38, fig. 1), the brain- 
cavity measures nearly twice the upper nasal length ; this is an early and also a Mavr- 
supial state of things, and would have been still more remarkable in an earlier embryo. 
The nasals have a very convex dorsal outline, and dip where they slightly overlap 
the frontals laterally ; they are in sutural relation with the deep facial plate of the pre- 
maxillaries and maxillaries (px., mx.) ; the upper edge of the former is extensive, being 
three-fourths as large as that of the maxillaries. Two-thirds of the exposed outer face 
of the maxillaries is suborbital ; a hollow, beginning in the premaxillary, runs along the 
maxillary up to the lachrymal (/.); near its end there are two small infraorbital fora- 
mina (V*.); the first hole is small on both sides ; they, however, are very variable, as in 
one adult Philippine Colugo, I find two openings on each side, and in another four on 
bl ara 2) 
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