DEVELOPMENT OF THE SKULL IN THE CROCODILIA. 279 
now more than twice as long as the parachordal tract. The whole base gradually 
lessens forwards, but at its middle, in the ethmoidal region, the lateral elements (tra- 
beculz, #7) cease. The intertrabecula then enlarges somewhat, gradually lessens again, 
and ends in front of its own crest, the septum nasi, in a spearpoint-like process, the 
prenasal rostrum (p.n), which turns a little downwards, and projects slightly beyond 
the nasal labyrinth. 
The flattened trabecule, after giving off the orbito-sphenoids (0.s), swell into a short 
solid wedge; the two wedges fill in the space between the hind lobes of the nasal 
capsule below: they are the cornua trabecule (c.tr). These cornua in short-faced 
forms, such as the Amphibia, spread into the fore face; here, in the race of growth, 
they are left midway by the fast-growing intertrabecular bar. 
The trabecule almost touch each other above, where they give off the orbito- 
sphenoidal wings (fig. 1, 0.8); these together form a lozenge-shaped hammock for the 
fore brain to lie on, and, whilst ending in a sharp point on each side in front, are tied 
by strong cartilaginous tapes to the posterior wings, or alisphenoids (a/.s). 
The large pyriform anterior fenestra, and the small oblong fenestra behind them, 
bring this skull very near that of the Lizard (“Skull of Lacertilia,” Phil. Trans. 1879, 
pl. 43). The ethmo-nasal crest of the middle bar (p.e) is exposed in its hinder part, in 
front of and between the orbito-sphenoids ; it there forms a sort of “ crista galli” between 
the olfactory lobes, that rest upon a concave part of the roof of the nasal capsules. 
This hinder, more swollen part of these capsules corresponds to the ethmoidal region in 
the Mammal, but is very simple within. After a sudden contraction the nasal roof and 
walls are enlarged again, sinuously, but, on the whole, are gently lessened up to their 
fore end. The olfactory nerves pass through a single hole on each side behind the 
higher part of the roof in the front of the rhinencephalic recess. The walls in the true 
nasal, as well as in the ethmoidal, region, pass across, below, and form a very complete 
floor, becoming confluent (as I shall show in the next stages) with the intertrabecule 
for some extent. 
In front, they are bulbous below, and the semi-distinct ale nasi (a/.n) form two upper 
bulbs twice as large as those below; these latter are perforated in their middle (above). 
This crescentic passage, with its horns looking backwards, is the external nostril (¢.n). 
Here the connate, circular, valvular fold is so specialized as to open on the upper 
surface of the head, whereas the primary position of the opening is below. 
The auditory capsules (aw) are only confluent with the rest of the chondrocranium 
below; they are very large, and have lost much of their original ovoidal shape. The 
semicircular canals (a.s.c, h.s.c, p.s.c) are large and shine through the unossified 
cartilage; so also do the other processes of the membranous labyrinth. A large 
pyriform tract of each capsule is seen on the upper surface of the skull; its narrow 
end is in front, and that part projects outwards, and is produced into an angle. 
VoL. X1—part 1x. No. 3.—October, 1883. 2x 
