776 
ME. W. K. PAEKER ON THE STRUCTURE AND 
Tinamus robustus, where the “fenestra” becomes a “notch” (Struthious Skull, Plate xv. 
fig. 8, c . f.c ), and T. variegatus, where it has not appeared, the skull in this respect being 
perfectly Struthious *. 
The distinction between the perpendicular ethmoid and the septum nasi is merely 
histological in the Mammal ; but here we see a true morphological cleft, which is now 
imperfect above and below, and never, in the Fowl, quite complete above, although this 
is common in the higher arboreal types. 
The vertical orbito-nasal septum has undergone fission between the eyes, as well as 
between the olfactory sacs : a considerable series of these clefts appear in this plate in 
some birds, all after one fashion; hut in the Fowl there are only two, and in the 
Struthionidae only one. This posterior cleft divides the ethmoid (eth.) from the pre- 
sphenoid Q?.s.) : this latter region is very feebly developed ; for the fenestrate cleft 
ends below at a great distance from the base, and the ethmoidal and basisphenoidal 
regions meet below it. 
The bar which encloses the anterior cleft below is very instructive ; it is at present 
of considerable thickness (Plate LXXXIII. fig. 2, s.v.l.), although it is absorbed in a 
few days after this period. It is alate ; and I propose to call the alar outgrowths the 
“ supervomerine laminae,” to connect them with their persistent and more largely 
developed counterparts in the Frog and the Crocodile. They have their largest deve- 
lopment behind (see Plate LXXXII. fig. 11, which shows them magnified 20 diam., and 
from below) ; the vomer commences below the middle bar at their front end (Plate 
LXXXIII. fig. 1, v.) ; when there are symmetrical vomers (as in Picus) they commence 
in the fibrous tissue below the laminae. The posterior edge of the nasal septum is also 
alate (Plate LXXXII. fig. 4, s.n.), and has, in front of the alee, an upper and a lower 
thickening, and a groove connecting these enlargements ; this is caused by the burrow- 
ing of the nasal nerve as it passes downwards and forwards. In fig. 4 the aliethmoidal, 
aliseptal, and alinasal outgrowths are cut away ( al.e ., al.s., al.n.) ; the rounded and 
flattened prenasal cartilage ( y.n .) is seen to have a somewhat downward direction. 
The rostrum, or “ anterior parasphenoid,” is still quite distinct from the ethmoid, and 
a little also from the front of the basisphenoidal region ; but directly beneath the optic 
nerves (2) it has grown into the substance of the cartilage, and the sella turcica is ossi- 
fying fast. The basitemporals (Plate LXXXIII. fig. 4, b.t.) are also rapidly coalescing 
with this common osseous mass, and they form a floor to the pituitary space ( jpt.s .) and 
also to the “ posterior basicranial fontanelle ” {jp.b.f.). The notochordal shaft is now 
fast developing into the basioccipital bone, which still encloses the starving remains of 
the notochord; behind, in the unossified condyle ( o.c .), it is still soft (figs. 1 & 4, n.c.). 
* This cranio-facial cleft (c./.c.) is a perfectly ornithic character, and in Tinamus robustus is a beautiful 
correlate of the segmentation of the shoulder-girdle across the glenoid facet and the acuteness of the angle at 
■which the scapula and coracoid are bent upon each other. On the 9 th day of incubation the scapulo-coracoid 
bar of the chick is falcate and partly segmented ; but by the time the cranio-facial cleft is well formed (14th 
to 16th day) the scapula has acquired a typical condition. 
