52 
]\IR. W. K. PARKER ON THE STRUCTURE AND 
edge, touching the top of the two united canals (tig. 4, p.s.c.). The angle between 
this short oblique side and the concave line of the base of the hone dips somewhat into 
the oblique deep fossa, which at this part divides each capsule from the proper occipital 
cartilage. The projecting points of each bone, on each side of the lower remnant of 
the suture, come within a short distance of the neatly circular, large foramen magnum 
( fm .). Between the convex, ear-shaped condyles (oc.c.), below, the basioccipital is seen 
( b.o .), and over, and outside the condyles, the squarish exoccipitals (see fig. 1, e.o .) are 
seen, creeping upwards towards the supraoccipital and outwards into the quite incon¬ 
spicuous paroccipital region. Outside that tract the epihyals and facial nerves ( e.liy ., 
VII.) are shown, and above them the oblique, massive, unossified auditory capsule, 
swelling with the large canals (op., p.s.c.). Already, so rapid is the ossification, the 
broadest part of the supraoccipital bone ( s.o.) is marked by an arched ridge for mus¬ 
cular attachment right and left of the mid-line ; these ridges are parallel with the 
lower margin of the bone. 
A vertically longitudinal section of this most instructive skull (Plate 15, fig. 5) shows 
the height of the skull cavity, whilst the embryo is still very immature, and the 
continuity of the marginal part of the cartilaginous skull-basin is still complete. As 
in the side view, the frontals, parietals, and squamosals (f, p., scj.) are seen, just 
meeting in their most projecting parts, but they fail to wall-in the skull. Already, in 
front, the frontals are very thick, and the nasals ( n .) also ; the middle vomer (v.) is 
short and stout, and the anterior paired vomers (v'.) are small, thin, curved, clavate 
bones. 
The septum nasi and perpendicular ethmoid (from a.l.n. to p.e.), together, form but 
a small, low, triangular wall, whose blunt apex is a tittle behind the middle, and 
scarcely rises into a cartilaginous crista galli. Altogether, this part of the skull 
is less developed than in the Armadillos. Between the partition of the snout and 
the proper septum nasi, there is a small oval fenestra (i.n.f.), with its long axis 
^lengthwise. 
The thick hind margin of the vertical ethmoid (p.e.) is grooved for the olfactory 
nerves, but the cribriform plate (cr.p.) is but tittle seen in this view ; between it and 
the orbitosphenoidal band (o.s.) there is a semicircular fenestra. The roof-cartilage is 
cut away ( al.n. to al.e.), and also the alinasal (cd.n.) itself, but its thickness is 
shown ; the base of the whole septum is thickened below by the great intertrabecula. 
This is shown as cut away from the presphenoidalregion (p.e., to b.s.), for in the hind 
half the section is in the middle, but in the fore half the basal part is left complete. 
Where the alinasal region ends, there the cartilage gives off a curious spoon-shaped 
retral process, the recurrent cartilage ( rc.c .) ; this is concave outside and convex 
towards the septum nasi ; it protects Jacobson’s organ, and so, also, does the tittle 
additional vomer (v.) seen on each side in this region. These parts are better seen 
below (Plate 15, fig. 6), which shows the broad, symmetrical floor of the snout and 
the lateral nostrils (n.f, e.n.). The floor is elegantly alate behind, and from each 
