58 MR. W. K. PARKER ON THE STRUCTURE AND 
the opisthotie region (op.). An oblique view is had, also, of the annulus tympanicus 
(a.ty.) with its related parts. 
The mandible (fig. 6) is shorter and stouter than in the embryo Unau (fig. 3), 
the coronoid process (c7.p.) is not so sharply divided from the articular or condyloid 
process (cd.p.), and the angular (ag.p.) is much deeper, further forwards, and has a 
larger crescentic notch between it and the condyloid part; the middle of these pro- 
cesses, only, is still capped with cartilage. 
Of the parts of the endocranium to be seen in this view, the snout (a/.n.) has already 
been described. Inside the orbit, the orbitosphenoid (0.s.) is partly seen, with the 
optic nerve (II.) emerging ; the upper border of this plate is indicated by dots along the 
orbital plate of the frontal. MxcKket’s cartilage and the manubrium of the malleus 
(mk.) are seen, and behind the large investing bones the massive occipital arch. 
The large supraoccipital (s.o.) looks like a continuation of the roof plates ; below it, the 
tract of cartilage is large, for the exoccipitals (e.0.) are small at present, they are 
creeping round the outside of the projecting condyles (o0c.c.). Where the epihyal 
passes off from the opisthotic region (op.) there some bony deposit has begun ; then 
the bar suddenly lessens and ossifies as the ceratohyal (¢c./y.), which is short, one- 
jointed, and is articulated to a shortish, thick, unciform hypohyal (h.hy). That 
segment is attached by its narrow distal end to the front of the U-shaped unossified 
basal pair; the thyrohyals (t.hy.) are mere spurs, the crura, of the U-shaped piece, as 
in the Unau, 
The end view of the skull (Plate 13, fig. 10) is much like that of the younger 
embryo of the Unau (Plate 8, fig. 4), and as in the latter the ossification is nearly as 
far advanced as in this much older embryo, it follows that the ossification is more 
rapid and intense in the other kind—the Unau. 
Signs of median subdivision are still evident in this large, roughly semicircular 
centre (s.0.), which has thoroughly ossified all the upper part of the large occipital plane. 
The lower angles are cut away, as it were, the shortened outline then running inwards 
and downwards ; thence the lower outline, sharply marked off from the cartilage, has a 
small median and two large lateral concavities. Here the foramen magnum (/:m.) is 
pyriform, the narrow part being above; the condyles (0e.c.) project well, and are 
flanked by the small exoccipitals (e.0.) ; 
> 
a very smal] tract of the basioccipital (b.0.) is 
seen in the fore margin of the great opening. The epihyals (e.y.), as they pass 
inwards and forwards, cover part of the shallow and narrow paroccipital region ; 
above, and outside them, the opisthotic region (p.s.c., .s.c.) is seen from behind. 
Covering the whole top and sides we see the parietals and squamosals (p., sy.). 
Part of a vertical section, taken left of the great septum (Plate 8, fig. 8, p.e.), 
shows this wall as a short low triangle, shorter than in the Unau, but higher (Plate 
15, fig. 5.). A small fenestra (7.n,f)—-very common in low Eutheria—appears near the 
end of the snout, dividing the septum nasi, proper, from the septum of the snout, where 
the alinasal tract (al.n.) ends below; thence the cartilage grows backwards as the 
