486 
MR. W. K. PARKER OK THE DEVELOPMENT 
The basi-hyal of Lepidosteus is remarkable for being very long and essentially double. 
There are only four perfect and one imperfect branchial arches ; the auditory capsules, 
at first, are as distinct as in the Tadpole, their basal region remains membranous for 
a good while, as in the Salmon. 
In embryos two-thirds of an inch in length, more than one-half larger than our first 
stage, the chondrocranium is larger and stronger, but has few fresh things in it. 
The trabeculae and palato-quad rate cartilages are still confluent, but the former 
are now some distance apart, the binding cells of the former stage being converted into 
a pyriform mass of true cartilage, with its broad end in front and projecting beyond 
the paired bands or trabeculae ; this is the intertrabecula. The pedicle of the suspen- 
sorium has applied the inner side of its apex to the most curved part of the trabecula, 
and an oblong joint is forming. 
A spike of cartilage has grown forwards from the auditory capsule over the hinder 
part of the superorbital region; this structure is seen temporarily in large larvae of 
Triton , and permanently in Siren. 
The divergence of the basal bands is now at its fullest, and the apex of the cranial 
notochord—one-third of the rod—is twisted, curves a little upwards, and is far from 
the moieties of the investing mass. 
In young Lepidostei, one-half larger than the last (1 inch long), the chondrocranium 
may be said to be complete, and free from intrinsic ossification, except in the sheath of 
the notochord, the eerato-hyal, and some parts of the branchial arches. 
The whole structure is much longer, but most of the increase in length is due to the 
development of the three basal cartilages in front of the cranial cavity. The occipital 
arch is perfect, and the tegmen from it runs well forward. 
The superorbital band is now perfect, and in front it passes into an anterior tegmen 
round the olfactory lobes, and the hemispheres, thus the cranial box is perfect there. 
But there is a large pyriform fontanelle below, a larger oval fontanelle on each side in 
the orbital region, and a still larger membranous space, the great fontanelle, above. 
The sudden and immense development of the precranial bars in so short a time is 
very remarkable; their relative massiveness makes this skull like that of a young 
Sturgeon five or six times as large. In that type the solid rostrum is formed of the 
two large trabecular cornua, which flank the still larger intertrabecula, like decurrent 
leaves. In the Sturgeon there is an antorbital expansion of the lateral ethmoidal 
region at the end of the rostrum, and each olfactory capsule lies close in front of the 
antorbital wall, as in a crypt. But in Lepidosteus the two capsules are carried away 
to near the end of the snout, and have no cartilage near them except the rostral bar, 
on each side of which they lie. 
Whilst the fore part of the chrondrocranium is like that of a young Sturgeon 5 or 
6 inches long, the cranium proper is like that of a Salmon ten or twelve days after 
hatching, when its length agrees with that of this stage of Lepidosteus, namely, about 
1 inch. 
