208 MR. W. K. PARKER ON THE STRUCTURE AND DEVELOPMENT 
that of the pig (“appendix ale nasi”), and protects the outer edge of the lip of the 
nasal sac (see “ Pig’s Skull,” plate 36. fig. 1, ap. a.n). Seen from above (fig. 2) the skull 
is a very elegant structure, with its approximated nasal roofs, its prow-like trabecular 
rostrum (d.¢r), its oval anterior remnant of the fontanelle, and its convex tegmen cranil. 
The superorbital ridges (s.od), so early seen in the embryo, now give character to 
the skull; they are grafted upon the otic capsules behind, and upon the nasal cap- 
sules in front, and even down in this type complicate the morphology of the ecteth- 
moid. A superorbital foramen opens out in the front part of the groove between the 
superorbital and the “tegmen;” and behind the tegmen are seen the right and left 
“aqueducts of the vestibule” (ag.v). On each side of these the elevation caused by 
the semicircular canals is clearly seen. 
A lateral view (Pl. XX XVIII. fig. 2) shows the relation of the parts very clearly, 
and especially lights up the wing of the “antorbital,” or “pars plana.” Although in 
the bird and mammal the antorbital cartilage is absent over the eye, yet it appears 
behind in the “sphenotic” region of the otic cartilage, and in front on the lateral 
ethmoid, running down in front of the eye as the free outstanding edge of the ect- 
ethmoid (‘“ Fowl’s Skull,” plate 81. fig. 5, p.p), whilst the “ tegmen cranii” reappears as 
the retral spike growing from the coalesced nasal sacs (ibid. plate 83. figs. 2, 4, 6 (eth). 
Here there is no distinction of orbital and larger wings of the sphenoid; the space 
between the superorbital and trabecular cartilages is filled in by a continuous growth 
of the same nature—a vertical sphenoidal wall, which is riddled with larger and smaller 
holes, the more important of which serve as landmarks for morphological territories 
(Pl. XXXVIII. figs. 2 & 4. 2, 5, 5°). 
Besides the olfactory fenestra, there is another between the partially fused trabecular 
cornua and nasal roofs (Pl. XXXVIIL. fig. 4, tr,f). The mammals do not show this; but 
in birds it is very common—a re-separation of the trabecule from the nasal znner walls ; 
it is not seen so low down as among the true “ Struthionide ” (“ Ostrich’s Skull,” plate 7. 
fig. 2, s.)—but appears in the next group, the Tinamous (ibid. plate 16, fig. 8, s.), 
and in the Fowl in the Tinamine stage. (‘‘ Fowl’s Skull,” plate 83. fig. 4, cfc). 
The Mammalian skull is markedly prefigured by that of the Shark in the pituitary 
region; there is an anterior and a posterior “ clinoid wall,” and a floor to the sella 
turcica perforated on each side by the internal carotid (Pl. XXXVIL. fig. 5, acl, p.cl, 
py, tc). This is quite unlike what is seen in Osseous Fishes, Lizards, and Birds, which 
have no cartilaginous floor to their “sella.” The notochord is replaced by cartilage ; 
and the articulation of the skull to the “atlas” is by two condyles. 
Between the superoccipital cartilage and the proper tegmen cranii above there is a 
crescentic fossa, looking forwards; on each side of this is the aqueductus vestibuli 
(Pl. XX XVII. fig. 2, ag.v). 
On each side of these burrowings are seen the anterior and posterior semicircular 
canals, the latter ending in the epiotic eminence. Outside the ampulla of the 
