DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
255 
opening—on its outer edge, and a small unfinished part behind that notch ; its 
general form is round and gently concave above and convex below, but it runs into 
crenations at the postero-external margin, and also (.Plate 38, fig. 1, a.ty.) is developing 
a process which is the rudiment of the compressed bony meatus externus (see Plate 38, 
fig. 4, a.ty). 
The end view (Plate 25, fig. 3) shows the imbrication of the roof-plates as they fit 
upon the occipito-auditory region; the parietals, interparietal, and squamosals 
{p., i.p., sq.) are thus seen, and the latter show their sinuous enlargements, due to the 
excavations within them. 
Endocranium of embryo of Galeopithecus volans ; 1st Stage (a). 
Many things belonging to the inner cranial structures can be seen in the dissected, 
but perfect, skull (Plate 37, figs. 1-3 ; and Plate 38, fig. 1); but only when the invest¬ 
ing bones have been removed are the deep parts thoroughly visible. 
Such further dissections are figured in lower and upper views (Plate 39, figs. 1, 2), 
with some of the investing bones, left for the most part in outline, to be useful as 
landmarks. 
The short, broad snout ( al.n .) has its nostrils (e.n.) near the end, and rather under¬ 
neath ; the snout narrows in front, broadens behind the nostrils, and then is some¬ 
what pinched in, 
From the middle of the floor, which crosses over the premax diaries (px), the 
recurrent cartilages (rc.c.) are given off, these grow round the opening of Jacobson’s 
organs and then run along on their inner and under side as them proper, but imperfect, 
capsule. These curious retral growths of the snout are twice as long in this species as 
is normal, a fact the meaning of which I cannot explain, but which will be understood 
when our knowledge of these parts is more advanced. 
The inferior turbinals ( i.tb.) are very feeble, but the foremost coil of the middle 
turbinal series ( m.tb .) is very large indeed—both in width and in length ; it extends 
forwards twice as far as usual: three other coils of this series are seen behind it. 
Above (fig. 2), in this species, the olfactory labyrinth ( al.e .) is seen to be short, and 
not very wide ; this is partly due to age, and is j)artly a specific distinction. The 
whole face being shorter and broader in this embryo than can be accounted for by 
difference of age ; the thick top of the septum (p.e.) does not end in a definite crista 
galli. The top of the great septum {p.e.) is very oblique, it is narrow, and has a 
smaller perforated plate {cr.p.), right and left of it, than is usual in Insectivores. This 
cribriform plate is quite unlike that of the Hedgehog or the Mole, and is quite like 
that of a young Frugivorous Bat ( Cynonycteris collaris), now before me. Its upper 
recesses are shallow, its size is small and sub-oblong—widest above—and its perfora¬ 
tions are comparatively few ; the Frugivorous Bat on one hand, and Cuscus on the 
other, gives us the two cribriform plates most like it. A tract of median cartilage is 
