OF THE MARSIPOBRANCH FISHES. 
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the rounded paired trabeculse, and that afterwards they flatten out, and it rises 
upwards to form the ethmo-septal partition of the nasal region (‘ Challenger Memoirs,’ 
vol. i., part 5, plate 2, figs. 3-7). 
This is the manner of growth seen in all Reptiles above Serpents, in Birds, and 
in Mammals. Here, in the lowest kind of skull we know of, the median prochordal 
cartilage appears as two tracts, one before the other, the two quite independent of 
each other, and very much unlike in form and consistency; so that the skull itself in 
thelMyxinoid is formed of separate segments, although the facial arches are not 
differentiated (or segmented) from the edges of the paired cranial bars. 
The long oval space in front of the short parachordal tracts, reaching from there to 
the ethmoidal commissure (Plate 10, figs. 1, 2, 3), is imperfectly closed below by a 
remarkable spoon-shaped cartilage of the soft kind; this is the hinder intertrabecula 
{p.i.tr .). Under the proper pituitary region, we see the bowl of the “ spoon,” which is 
rostrate and perforate behind ; the straight, narrow “ handle ” runs forwards, touching 
the ethmoidal commissure : it gently lessens from behind, forwards. The handle 
leaves a large unfloored space right and left; it is gently scooped above, and the 
“ bowl ” considerably; this lamina is of even thickness, and is quite convex below. At 
some height above the end of the handle, a new cartilage begins, very different from the 
last; this is the front intertrabecida (a.i.tr.). This bar is composed of hard cartilage ; 
it is compressed vertically, is as wide as the handle of the “ spoon,” but higher than 
wide ; it is thickest behind, where it is emarginate and acutely bilobed ; and it narrows 
gently forwards, and is then thickened again. This “ front intertrabecula ” is one-sixth 
longer than the other, and more than its hinder fourth lies on the ethmoidal commissure, 
and under the long nasal labyrinth (n.a., e.n.t.). These structures are cpiite unlike what 
is seen in the Lamprey, where the cornua trabeculae are connate, and abort the front 
intertrabecula, and where the hind intertrabecula is composed of hard cartilage, and is 
only distinct fora very short time after metamorphosis (Plate 10, figs. 4, 5 , p.i.tr.). 
The state of things seen in Myxine is evidently due to the intense specialisation of a 
type, which, on the whole, does not rise above the level (or platform) of an Ammoccete. 
Some other “ novelties,” quite equal to this, will be seen as we proceed. 
Below the middle of the auditory capsule (Plate 9, fig. 2, cm.), there is a round 
fenestra ( m.hf ), half as large as the reniform subocular space (s.of) ; and below this, 
separated by a thick bar, is another oval space (If 2 .), twice as large as the subocular. 
These, also, are nascent segmentation lines, arrested and widened out. The bar 
bounding the little upper space, behind ( h.m .), is quite similar to, but wider than, the 
one in front—the pedicle (pel.) ; it is also composed of soft cartilage, whilst the thick 
bar running backwards from the pterygoid region under the reniform, and round and 
over the oval, fenestra, is hard cartilage. The narrow end of the oval fenestra looks 
upwards and forwards, and the hard bar below and in front of it, which lessens, and then 
widens out again, is the pterygo-quadrate bar, ending below, not in a quadrate condyle, 
but in a thin, inturned edge, somewhat rounded in outline. The hard cartilage ends. 
