DEVELOPMENT OE THE SKULL OE THE COMMON FEOG. 
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the basioccipital ( b.o .) ; so that during development it has remained true to its original 
character. 
The rest of the bony centres may be studied as part of the endoskeletal skull ; they 
are shown thus in the figures (Plate VII. fig. 10, Plate VIII. figs. 9, 10, Plate IX. figs. 1-9, 
Plate X. figs. 7-10), which represent them both from the surface and in sections. 
When the paros toses are removed from a partially macerated skull, a very remarkable 
osseo-cartilaginous structure remains (Plate IX. fig. 6, upper view, and fig. 7, lower 
view) ; for whilst the cranium itself is like a flat-bottomed boat, the superpalatals near 
the front, and the auditory masses behind, project like two pairs of out-riggers. 
These projections are connected together by the bowed pterygo-palatal bars ; and the 
quadrate dips its condyle outwards, backwards, and downwards. Forth standing from 
the fore end of the skull we see a symmetrical pair of chambers ; these are continuous 
above and below, and are parted by a septum (Plate X. figs. 3 & 7, s.n.), the “septum 
nasi;” the whole structure, seen from above and below, is ox-head-shaped, the “horns” 
being, each, the main lobe of the right and left emarginate snout-cartilage, the axis of 
the premaxillaries, the only free part of the “cornua” of the trabeculae. 
Both above and below (figs. 6 & 7, sn.c.), these sessile snout-cartilages send back a retral 
process which has a valvular relation to the nasal openings, outer and inner, partly 
closing the opening on its outer side (Plate IX. figs. 6, 7, v.e.n., v.i.n.). 
On the inner side of the inner nostril there is another valvular process (fig. 7, i.v.p.) ; 
this is better seen in the more enlarged figure and in the sectional views (Plate X. figs. 3, 
4, 5, i.v.p.) ; it is a small curved horn of cartilage with a broad fixed root in front. 
The transverse anterior margin of the nasal labyrinth is elegantly crenate, and the 
cartilage, both above and below, is partially hardened by endosteal bone on its superficies ; 
the mid line is gently concave, both above and below (Plate X. fig. 7). The nasal roof 
is made by the “aliseptal” laminte (al.s.), the floor by the “subnasal” or trabecular 
laminae ( s.n.l .). 
The external nostril is surrounded below and behind by the “ alinasal lamina” ( cd.n .), 
which has greatly changed from its condition in the 7th stage (compare Plate VII. fig. 11, 
and Plate IX. fig. 6, cd.n.) ; for this curled cartilage was relatively very large, and articu- 
lated behind with the ethmoid above the superpalatal bar ; but now it is small, has be 
come more freely segmented from the nasal roof, and the part which articulated with the 
ethmoid turns forwards and has a free notched end. There are no turbinal outgrowths 
in the Frog’s nasal capsule, and yet it is very complicated anteriorly ; this complication 
is septal, and does not arise from the “ alee,” as is the case with true turbinals. A 
transversely vertical section (Plate X. fig. 3) through the outer nostrils displays an unex- 
pected number of laminae, which I have only been able to understand by reference to what 
takes place in higher types. The section has been made exactly through the external 
nostril (e.n.), and close to the fore edge of the internal nostril (see Plate IX. fig. 7, i.n .) ; 
it has passed through the nasal process of the premaxillary (n.px.) above, and through 
the palatal process (p.px.) below. The aliseptal lamina (al.s.) is here at its narrowest, 
MDCCCLXXI. 2 B 
