OP THE SKULL IN LEPIDOSTEUS OSSEUS. 
469 
it forms a loose joint inside the hyomandibular by its narrow upper end; and below, 
its inner face is scooped for the backwardly bent head of the cerato-hyal ( c.hy .). 
That segment is seven times the size of the inter-hyal joint; its head is bent back, 
its shoulder thickened, and has a short, separate ossification, the epi-hyal (e.hy.), and its 
shaft is rounded. The inferior condyle is hemispherical, and the main part of the 
thickest rod is ossified as the cerato-hyal (c.hy.). 
The hypo-hyals (Plate 34, fig. 4, h.hy.) are sub-globular nodules, scooped above for 
the cerato-hyal, and ossified on their outside. They fit against the paired concavities 
of the basi-hyal ( b.hy.) —a double, oblong, tongue-shaped, interglossal segment, as 
long, and twice as wide, as the cerato-hyal. This thickish plate is grooved above and 
below, is rounded and emarginate in front, and is composed of a spongy kind of cartilage, 
full of fibrous septa, which form a network in it. 
There are four perfect, and one imperfect, branchial arches; they are less than half 
as solid as the hyoid (Plate 34, fig. 4, br). In the mandibular arch, when the mouth 
is closed, the axes of the suspensorium and its free cartilage become coincident. In 
the hyoid arch they are parallel, not coincident; here, in the branchial arches, they 
are continuous, the upper being superimposed upon the lower element. 
The relative size of these parts is greatly altered, and the subdivision does not 
exactly correspond with that of the mandibular and hyoid. The part answering to the 
suspensorium and hyomandibular is less than a fourth the size of that which corresponds 
to the mandible and cerato-hyal. Each “ pier ” is subdivided into two pieces—a 
pharyngo-branchial (p.br.) above, and an epi-branchial (e.br.) below. The upper piece 
is a little tongue of cartilage, turned inwards and forwards, and the lower has a short, 
bony shaft, and is a little rod turned directly downwards. These two segments do not 
correspond with the hyomandibular and symplectic ; the upper piece has a double 
counterpart in the hyoid arch, namely, the hyomandibular and symplectic—one 
cartilage, with two bony centres in it. 
Also, the counterpart of the cerato-hyal, the cerato-branchial ( c.br .) articulates 
directly with its pier, the epibranchial; so that there is nothing in the branchial arches 
corresponding to the inter-hyal. 
Instead of the hypo-branchials (h.br.) being short nodules, they are in the first two 
arches nearly as long as the cerato-branchials ; are thicker than them below, but less 
ossified. The three joints between the four pieces seem to show no distinct joint- 
cavity, but are fibrous. Below, the rounded rods of the hypo-branchials fit into depres¬ 
sion on the basal bar—basi-branchial ( b.br .). This is, in front, a thickish, rounded rod 
of cartilage; it then thins out, and behind it is flat and emarginate. The first and 
second arch unite with the long, first basi-branchial. segment; the third nearly reaches 
the short second piece,'and the fourth is loosely attached to the side of the third piece, 
which is as long as the first. None of these pieces are ossified, and the first does not 
reach the basi-hyal, for the hypo-hyals are thrust between them. 
The lessening third and fourth hypo-branchials (h.br.) are not ossified. The fifth 
