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MR. W. K. PARKER OK THE STRUCTURE AND 
D. Transversely-vertical sections of the head of a young Sturgeon 8 inches in length. 
These sections show much clearer signs of the composition of the great ethmo-nasal 
tract than can he got from the outside views of dissected skulls ; moreover, they 
display the curiously cancellated and burrowed condition of the very hard hyaline 
cartilage. There is generally some fatty tissue imbedding the vessels that run in 
these burrows and spaces. 
Section 1.—The first of these (Plate 15, fig. 14) is through the end of the beak, and 
the “ prenasal rostrum/’ or intertrabecula (i.tr.) is depressed or spindle-shaped in 
section ; rough dermal bones are seen surrounding it. 
Section 2.—In the next (Plate 15, fig. 15) the cornua trabeculae (c.tr.) are cut through 
at their fore end; they are depressed at this part, sub-concave above, rounded below, 
and attached by a narrow isthmus to the top of the intertrabecula (i.tr.) which is 
sub-triangular here, and dilated and convex below. A rounded chink separates these 
three pre-cranial elements almost to their roots. The dermal bones form a flat upper, 
a round lower surface, and a lobate side. 
Section 3.—Here (Plate 15, fig. 16) the three elements have become fused together, 
but the burrowing vessels and the fatty tissue show the original line of union of the 
parts. The form of the triple rostrum is, above, concave at the middle, and convex at 
the sides; below, concave laterally, and convex at the middle. 
The dermal covering takes the same form, but the sides are notched ; here, as in 
the last, a sub-marginal groove, right and left, appears, below. 
Section 4.—Here (Plate 16, fig. 8) the enlarging beak shows a more rounded 
cartilaginous pith, but is very similar to the last; this is more than half way to the 
nasal capsule, behind. 
Section 5.—In this (Plate 16, fig. 9) the rostrum, close in front of the nasal capsules, 
has become multiangular; the cornua trabeculae (c.tr.) are again united merely by 
an isthmus to the intertrabecula mass; they are thick, almost bilobate, and descend 
obliquely; they are separated by a semicircular notch, laterally, from the middle part 
(i.tr.) ; below, also, a similar concavity is seen, right and left, but twice as large as 
those on the sides. Between the latter the intertrabecula is a rounded beam ; above, 
it is concave, and on each side has a lateral angle which bounds the lateral notch. 
The bones outside carry out this ridged form ; below, a thick squarish mass of bone is 
seen, which is one of the vomerine series (v.). 
Section 6.—Here (Plate 16, fig. 10) the olfactory sacs (ol.) are cut through their 
middle, and here the angulation of the parts is intensified ; the cornua trabeculae (c.tr.) 
are now large wings, pedate at their free ends, and are separated laterally from the 
intertrabecular mass (i.tr.) by a very large semi-circular notch, in which the nasal 
capsule lies. Here the intertrabecula forms a roof over the sac, right and left, and it 
is very hollow above ; below it is burrowed by a vomerine scute (v.), and is becoming 
