DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
263 
and fenestra rotunda ( fs.o.,fr.) —in the auditory capsule, the outlet for the facial, glosso¬ 
pharyngeal, vagus, and hypoglossal nerves (VII., IX., X., XII.) ; a bristle shows the 
opening from the ear-drum into the labyrinth of air-cells in the squamosal (sq.). 
The end view of the skull, younger specimen (Plate 37, fig. 7), shows the well-built 
occipital arch, with its elements distinct; the large foramen magnum, the outstanding 
condyles (oc.c.), and the mastoid process (op.) all well set in under and within the 
great investing plates. 
There is a remarkable difference between the hyoid arch in the lesser and larger of 
these young Philippine specimens (Plate 38, figs. 6 and 8). 
In the former (fig. 6) this part is not so well developed in some respects as in the 
embryo of the larger species, for the hypohyal h.hy. is not segmented off from the 
ceratohyal (c.hy.), whilst the latter region is not ossified, but the hypohyal region 
has an oval centre. The basal and tliyrohyal regions have now each a small bony 
tract. 
In the larger young (fig. 8.) these parts are much more advanced, and the hypohyal is 
segmented off from the ceratohyal ; each of these is rapidly ossifying, and so are the 
basal piece and thyrohyals; but these are continuous in the cartilaginous interspaces. 
Stage 4, d. — On the skull of the adult Galeopithecus philippensis. 
This is one of the most remarkable skulls to be found in the whole of the Eutherian 
division of the Mammalia; it is, thus, like the skull of a Serpent—a low type, and 
yet specialized, in its own way, to the uttermost. Just now, I am only responsible for 
the skull; the structure of all the rest of its organization must be accounted for and 
argued about by others ; but I must mention the size of its brain-cavity (Plate 39, 
fig. 3), as showing how small a brain this creature has. The proportion that the 
foramen magnum bears to the greatest intercranial breadth will serve my purpose, 
as I cannot go further into that matter. In the adult Galeopithecus philippensis 
and in the sub-adult Cuscus maculatus, that opening is two-fifths the greatest breadth 
of the skull inside ; in Lepilemur mustelinus it is only one-third, and in Loris gracilis , 
and Pleropus medius, only one-fourth. 
In the cranial characters that have been already described in the young specimens 
and embryo, I have shown that there are several things that are manifestly Meta- 
therian, but these are not the same things as those that show a Marsupial affinity in 
the Hedgehog and its allies ; they belong to another set of parts. 
I have already spoken of the help the young of Cuscus maculatus —one of the 
lowest and most generalized of the Eastern Marsupials—has been to me in the study 
of the growing skull of the Colugo. I now find that with the adult skull ot that 
species, and the adult skull of a great Frugivorous Bat (Pteropus medius) I have 
the two extremes, with the skull of Galeopithecus half-way between them. Not but that 
this bizarre type has its own unique characters; this might have been expected, for it 
