OF THE SKULL IK LEPIDOSTEUS OSSEUS. 
461 
double, and is as long as the cerato-hyal. The subdivided, ossifying branchial arches 
will be described in the next stage. 
The uniformity of the rapidly elongating intertrabecula is shown in the vertical 
section of the skull (Plate 32, fig. 4, i.tr.). The three trabeculae are shown inside the 
lengthening snout, with' its four rows of mucous glands in a second upper view 
(Plate 32, fig. 5) ; and in it, also, the position and relation of the sense-capsules and 
brain are displayed, and also how that the tegmen cranii ( t.cr .) leaves the large mid 
brain (C 2 .) unprotected. 
A partial view of the chondrocranium, namely, the floor, from its upper face up to 
the end of the cranial cavity (Plate 32, fig. 3) shows the huge notochord (nc.), whose bony 
sheath is incomplete above, and the fore end of w T hich is free, and but little attenuated ; 
that part is curved but little upwards (see Plate 32, fig. 4). The fusion of the basal 
bands and auditory capsules is shown to be perfect, and the cupped tracts for the 
ampulla of the posterior canal ( p.s.c .) and for the sacculus (vb.) are also seen. In 
front of these, on each side of the diverging parachordals—now to be called 
trabeculae (tr.) —the basipterygoid peduncles (b.pg.) are shown. In the emargination 
behind these, in the fore part of the ear-capsules and in the occipital ring, thin films of 
bony matter are forming, which will become the alisphenoids, prootics, and exoccipitals ; 
these will be shown better in the sections. The huge lanceolate pituitary fenestra 
(py) is floored by the parasphenoid ( pa.s .), which wedges in, in front, between the 
converging trabeculae. In front of that part the chondrocranium is complete. The 
olfactory nerves (I.) escape from the bulbs (Plate 32, figs. 4, 5, C 16 .) and run along to 
the distant nasal sacs (ol.) between the intertrabecula and cornua trabeculae in the 
deep groove between them above. The nasal branch of the ophthalmic (5') runs 
forwards outside these. Some of the bony plates are shown on the chondrocranium ; 
the foremost of these is the first of the maxillary chain (figs. 1, 2, mix'.) ; and on 
the palato-pterygoid there are three “ parastoses,” namely : the palatine, pterygoid, 
and mesopterygoid (Plate 32, figs. 1, 2, pa'., pg., ms.pg.). 
Transversely vertical sections show much that is instructive in this stage also (see 
Plate 33, figs. 1-13). 
Section 1.—In this (Plate 33, fig. 1) the fore end of the long face is seen to be convex 
above and somewhat concave below. The skin is very thick and glandular ; the nasal 
sacs (ol.) are simple pouches, with a thick epithelium, the tissue beneath the skin has 
now become osseous; in this way we get the premaxillaries, nasals, maxillaries, pala¬ 
tines, &c.; the plates directly over the nasal sacs are the nasals, and the palatine part 
of the premaxillaries is shown below the sacs. In this section we see the fore end of 
the prenasal cartilage or intertrabecula (i.tr.) ; it is a long oval in section, with the 
narrow part below and the sides compressed. 
Section 2.—Here (Plate 33, fig. 2) we have the prenasal (i.tr) cut through behind the 
nasal sacs; palatine teeth attached to bony laminae (pa.) are seen below, and similar 
