452 
MR. W. K. PARKER ON THE DEVELOPMENT 
lour, and is permanently arrested as the “ inferior pharyngeal; ” it is simply a short 
cerato-branchial. 
The four well-developed rods are not yet segmented across into the normal pieces; 
they are oval in section, pointed above, and rounded below, where they articulate with 
the common basi-branchial ( h.br.), which is one-third thicker than the arches. This 
conjugating rod is somewhat flat; it is thickest in front, where it fits by a rounded 
end between the hypo-hyals, and flat behind, where it projects beyond the arches. 
Third Stage .— Young Lepidostei, to 8 lines long. 
In young individuals about two-thirds of an inch (16 to 17 millims.) long, the 
cartilage has become quite consistent, and some parts not chondrified in the last stage 
have become solid. 
The head (Plate 30, figs. 5, 6) has straightened out considerably, and the basis cranii 
bulges below; but the sharp, recurved fold under the mid brain, where the fore and 
hind brain approximate, although a mere chink, is ineradicable. 
The round and curiously mammillated snout is much smaller now, relatively; the 
notochord ( nc .) has retreated considerably; the pituitary body ( py. ) is still separate 
from the infundibulum (inf.). 
The azygous trabecular bar (figs. 7, 8, i.tr.) now shows itself in sections taken 
vertically through the head, but all the rest of the basal cartilage is far from the mid 
line. The notochord (nc.) is very large, and descends considerably beneath the swelling 
hind brain (figs. 5, 6, C 3 .). Below the mouth and throat, the fore end of the mandible is 
seen in the right section (Plate 30, fig. 5 ,mk.); it contained more than half of the head 
above, and less than half below; thus that rod, and the rest of the post-orals (hy. } 
hr 1 ' 4 .), are cut through a little on the right side of the middle. But in the left half 
(Plate 30, fig. 6), the median rods ( h.hy ., hr 1 ' 4 .) are brought into view, below; above, the 
junction of the trabecula with the palato-quadrate (tr., p-jpg.) is seen; this, however, had 
to be exposed by dissection; the sub-ocular space is seen as a crescentic gap with its 
convexity downwards. 
The chondrocranium is figured as seen from above and below in a dissection of a 
somewhat larger specimen (8 lines long) ; it is much more perfect than in the last 
stage (Plate 30, figs. 3, 7, 8). 
A full third of the cranial floor is membranous; the side walls are membranous in 
front, and are made by the auditory capsules behind; but a rudiment of the roof or 
“ tegmen cranii ” is now found, right and left. 
The thick cranial notochord (nc.) is only half the length of the chondrocranium, 
now; it is somewhat moniliform, lessening by three successive stages, and is bent a 
little in this specimen to the right. 
The narrow part is rounded at its end, and ascends but little into the clinoid 
fissure (Plate 30, fig. 5, nc.) ; a third part at least is not invested by the parachordal 
cartilage (iv.). 
