654 
ME. W. K. PAEKEE ON THE STETJCTUEE AND 
of the Batrachian type of skull, if we make allowance for the absorbed floor-plate. 
Yet at once we see a modification, for the occipital condyles ( oc.c .) are more outside 
than behind. The absorption of the cartilage in front of the notochord takes place 
wittingly, as it were ; it has marked out, again, the parachordal region ( iv .) by absorption 
of the apices of the trabecula (see Plate 55. fig. 1, tr.) along with the newer cells of the 
pituitary floor. The notochord ( nc .) is but little diminished ; even now it lies mainly 
over the parachordal floor behind, and is free over the parasphenoid in front. On each 
side a fissure marks the almost absorbed auditory cartilage from the parachordal plate, 
and in front of that chink the auditory, parachordal, trabecular, and mandibular carti- 
lages are all confluent, and form a gnawed tract on either side. Just where the optic 
nerves (2) pass out, there the trabecula is reduced to its primary size. But from thence 
each bar rapidly widens, running inwards to meet its fellow, and to form the ethmoidal 
floor : on this floor lie the olfactory lobes and the anterior fourth of the hemispheres 
(C 1). This zone is narrow above (fig. 5), and is there to be seen as the elegant 
arcuate front and junction of the steep side walls, which thin out extremely before they 
pass into the crest which runs from the auditory capsule (fig. 5). The ethmoidal belt, 
in front, grows into a median crest or keel and a pair of side wings : the keel is the 
septum nasi with its “ cornua ” ( s.n ., c.tr.), the side wings belong to both the trabeculae 
and the palatines ( e.'pa .). 
This keel, and these “ horns,” are explained by the early stage (fig. 3), and they serve 
as a key to open the mysteries of the adult skull at this part (Plate 62). In front of 
the palatine conjugations the trabecular internasal plate has been reduced to less than 
one fourth of its former width (figs. 3, 5, 6). This narrowing produces a large crescentic 
notch on each side, which is, externally, the hind margin of the inner nostril. The 
subnasal lamina, or primary trabecular commissure, dilates twice, beyond the middle 
and in front, but is nowhere wider than the same winged part in a Passerine bird. In 
front the septum is broad, for the internasal plate there grows up into a wall, the rudi- 
ment of the alinasal laminae ; from this wall, above, the cornua trabeculae pass backwards : 
the stem and the arms of this structure look like a miniature of the “ governor ” of a 
steam-engine. 
When this fore part is cut through at the front of the septum nasi and in the roots 
of the “ cornua,” then it is seen that the septum is a thick and high wall, and that the 
rudimentary alae nasi (fig. 8, s.n., al.n.) are also thick, and have rounded inferior edges, 
Above, from the very narrow aliethmoidal bands ( al.e .) to the front, the aliseptal plates 
( al.s .) are scarcely at all produced right and left (Plate 61. fig. 5). 
The backgrowing “ horns ” of the trabeculae (Plate 60. figs. 5, 6, and Plate 61. figs. 
4, 5, c.tr.) form a small angle with the septum, and have a knobbed free end ; they 
grow from the upper part of the intemasal plates, and therefore lie nearly as high as 
the roof of the septum. The foliaceous prepalatine (pr.pa.) runs forwards outside, and 
parallel with the trabecular horn, but free of it, instead of being nearly flush with it 
and more or less coalesced, as in the embryo (fig. 3 ,p.n.l.). 
