OE THE SKULL IN LEPIDOSTEUS OSSEUS. 
455 
(h.hy.), the thick, semi-globular, distal segment of the arch. The basal piece, glosso- 
vel basi-hyal (b.hy .), is wide, oblong, and three-fourths the height of the cerato-hyal; 
its rounded fore end is rather blunt; it is, in reality, a double bar, and its tissue is 
much lighter and more spongy than that of the side bars ; its posterior end is doubly 
scooped for articulation with the hypo-hyals. 
The branchial arches (Plate 30, fig. 8, hr'.) are now beginning to divide across into 
four pieces on each side, namely, a pharyngo-, an epi-, a cerato-, and a hypo-branchial 
(see Plate 31, figs. 12, 13); a rod of cartilage of about the same thickness as the 
arches runs along the mid line, connecting them together; this is the basi-branchial 
( b.br.). 
Transverse sections of a somewhat younger specimen (7\ lines long) show much that 
is instructive, and corroborate the observations made upon dissected embryos. 
Section 1.—The first of these (Plate 31, fig. 1) is in front of the chondrocranium, 
through the fore part of the nasal capsule ( ol .). The skin is very thick, and the 
mucous membrane of the nasal sac is composed of large columnar cells. The upper 
part is much flatter than the lower, in which three of the suctorial disks ( s.d .) are seen 
in section. 
Section 2.—The next section (Plate 31, fig. 2), is through the middle of the nasal 
sacs (ol.) and the fore-part of the hemispheres (C la .); here the lower face is less 
convex and the upper more so; the fore end of each trabecula (c.tr.) is cut through; 
it is a rounded projection, the rudiment of the free cornu. 
Section 3.—The third section (Plate 31, fig. 3) is through the back of the nasal 
sacs (ol.), the first third of the cerebral hemispheres (C la .), and the solid coalesced end 
of the triple trabecular outgrowths of the basis cranii. The outline of the trabeculae (tr.) 
is clearly seen below ; but above, these bars—which are oval in section at this part and 
very thick—are confluent with an upper median mass, the intertrabecula (i.tr.) ; this 
is wider than the paired bars, fits in and on them, and rises over them as a dilated and 
concave floor to the membranous floor of the cranium. 
Section 4.—The fourth section (Plate 31, fig. 4) is through the hemispheres (0 la .) and 
barely misses the eye-ball (for ol. read e.). Here the fore end of the palato-quadrate 
cartilages (p.pg.) is cut through, where these bars run into the trabeculse (tr.). The 
intertrabecula (i.tr.) is wider and flatter, and the shallow sulcus between the paired 
trabeculse is gone; they together form a convex mass below, at this part. The 
section of the palatines would be circular, but the conjugational band is very thick, 
and obscures their real form. 
Section 5.—The fifth section (Plate 31, fig. 5) runs through the fore part of the eye¬ 
balls ( e .). This section is at the end of the intertrabecula (i.tr.), and the trabeculse and 
palatine bars (tr., p.pg.) are only half as large as in the last, and this section is seen to 
be oval, for the connecting cells are much reduced in quantity. 
Section 6.—The sixth section (Plate 31, fig. 6), a little farther back, shows an evident 
fissure between the trabeculse (tr.), which are now flatter, like bricks, and the connect¬ 
ing band is so thin as almost to set the palatine band (p.pg.) free. 
MDCCCLXX XII. 3 N 
