OF THE MARSIPOBRANCH FISHES. 
413 
craniofacial skeleton ; the facial parts being such as are developed inside the remnants 
of the pleuro-peritoneal space, which for a time remain as the “ head-cavities.” 
The cranial part of the notochord (Plate 18, fig. 4, nc.) is twice as long as in the 
Mjxinoids (Plates 9, 10, 16, and 17), for the invested apex can be seen projecting into 
the small sagittiform pituitary space (“ basi-cranial fontanelle,” b.c.f.), so as to be 
further forwards than the hind margin of the sub-ocular fenestra ( s.of ). the apex 
turns upwards (fig. 5, nc.), and this part is invested by the hardened parachordals, 
which end as hard cartilage in front of the hind face of the auditory capsules (fig. 4, 
iv., cm.), but send backwards, below, paired spurs up to the point where, in a Tadpole, 
the occipital condyles would be formed. The cranial notochord becomes invested by 
cartilage equally above and below (Plate 22, figs. 2-6), and thence, outside, the 
cartilage thickens and extends right and left, until, reaching the auditory capsules, it, 
for a considerable extent, underfloors them. Here, however, there is no facial bar 
growing out from their outer sub-auditory edge as in the Myxinoids (Plates 9, 10, 16, 
and 17, au., iv., hm.). Where the investing mass (parachordals) passes into the 
trabeculae (iv., tr.), there the basi-cranial cartilage does extend itself into a facial 
outgrowth—the pedicle (pd.). 
In front of these outgrowths the basis cranii has an elegant, narrow waist (fig. 4), 
bounded by the narrow hind part of the trabeculae (tr.), which have a membranous 
tract right and left of them, and also between them (s.of, b.c.f.). The middle or 
“pituitary” space has opened to let out the posterior nasal canal (Plate 23, fig. 1, 
p.n.c.), which passes, widening towards its enlarged blind end, under the cranial 
notochord. 
From this point the trabeculae diverge, and the space left between them is filled in 
hy the hind intertrabecula (Plate 18, fig. 4, and Plate 10, fig. 5, p.i.tri), which is 
everywhere confluent with them, except where vessels pass through. 
The proper basis cranii is finished in front by the confluence of these three bars, and 
this solid ethmoidal region has a convex outline in the middle, which outline is made 
sinuous by a retreat of the edge, right and left, where the ethmo-palatine bars have 
grown on to the trabeculae (ep.a., tr.). This whole floor is concave below, although 
its middle plate was convex at first, for the pterygo-palatines, like “flying buttresses,” 
drop down, rather suddenly, and thus form an arched, or roof-like structure. A narrow 
sinuous band of soft cartilage runs along the front of the skull (ethmoidal region, eth.), 
and then hard cartilage breaks out again, in the form of a large shield, which is hollow 
below, sinuously convex above, notched in front, and at the middle as wide as the 
skull with its flying buttresses. No one familiar with the skull of Tadpoles can for a 
moment hesitate to call this the common “trabecular cornu.” In the huge Tadpole’s 
skull (Pseudis, my first stage, Phil. Trans., 1881, Part I., Plate 2), the cornua are 
united in their hinder half, but in an older Tadpole (Plate 11, figs. 1-3) they are only 
separated by a notch in front, sharper, but no larger, than the emargination on the 
fore-edge of this so-called “ posterior dorsal cartilage ” of the Lamprey. 
MDCCCLXXXIII. 3 H 
