470 MR. W. K. PARKER ON THE DEVELOPMENT 
cerato-branchial (c.br 5 .) is Jess tlian those in front of it; it is not ossified, and there is 
no other segment in that arcli. 
The branchial arches are but little modified after this ; they merely increase in size, 
and are always small as compared with the arches in front of them. A series of 
sectional views will complete the illustrations of this stage. 
I have now to illustrate this stage by a series of sections made from a specimen 
2^ inches long. 
Section 1.—This section (Plate 33, fig. 14) is taken from near the end of the snout 
in front of the nasal sacs. The intertrabecula (i.tr.) is seen to be oval, with the larger 
end below. The whole snout is elliptical, with a slight convexity above, and a slight 
concavity below, at the mid line. The premaxillaries (pxi) are cut through, both in 
them body and their palatine process (p.px.) ; they are reticulations of thin laminse, and 
both above and below enclose a mucous gland. 
Section 2.—TJre nasal sacs are cut through here (Plate 33, fig. 15, ol.) and the bony 
laminae are more complex; the intertrabecula (i.tr.) has the same shape as in the last, 
but the whole snout is rounder above and flatter below. 
Section 3.—Behind the nasal sacs other bones come into view (Plate 33, fig. 16); 
here the evenly elliptical rostrum (i.tr.) has the laminae of the ethmo-nasal (et.n.) sur¬ 
rounding it, and on the side a mucous gland is seen in the upper half of one of the 
maxillary chain ( mx .) ; here the lower face of the snout is becoming convex, with a 
median groove ; above this, right and left, vomerine teeth (v.t.) are seen. 
Section 4.—In this section (Plate 35, fig. l) the lower jaw also is cut through ; the 
snout is flatter here, has a ridged lip, right and left, with sub-marginal grooves. 
The intertrabecula (i.tr.), half-way between its fore end and the cornua (Plate 34, 
figs. 1, 2, c.tr.) is circular hi section, and is flanked by the layers of the thickening 
ethmo-nasal (et.n.) : outside, one of the maxillary chain (nix'.) is seen lying over the 
palatine (pci.), with its large tooth, and under the rostrum the two vomers (v.), each 
with a small tooth, are cut through. Below, the mandibular rods (mk.) are cut 
through at their front part, and right and left we see the solidifying substance of the 
dentaries (cl.) ; over the cartilage towards the mid fine, a small, separated style is cut 
through—this is the splenial (spi). 
Section 5.—Another section in front of the angles of the mouth (Plate 35, fig. 2) 
brings the tongue into view. Here the rostrum (i.tr.) is deep, and twice the size it had 
in the last section ; it is flattisli above, and more convex below. Here the loose reticula¬ 
tion of the extremely thin bony laminae w r ould seem to defy interpretation; but it 
can be classified into groups, and these groups named. Under the flat top of the beak, 
on each side of the rostrum, several of these thin plates are seen to be connected 
together, overarching a mucous gland (rn.g.) above, and the olfactory nerve (I.) lower 
down. Above these is a sub-marginal groove, right and left; outside this groove the 
beak is convex, and from the convex part there runs inwards a thin bony flake towards 
