OF THE MARSIPOBRANCH FISHES. 
421 
b. The skeleton of the fimbriated valve betiveen the mouth and pharynx. 
This peculiar structure, formed during metamorphosis, is figured, as seen in a 
vertical section of the adult P. fiuviatilis (Plate 23, fig. 1); from above, in situ, in a 
head cut through horizontally (Plate 23, fig. 2) ; and as removed from most of its 
surroundings and seen from above (Plate 14, fig. 8). 
The skeleton of this valve is shown in the upper view of the basi-hyal (Plate 18, 
fig. 7, and in Plate 10, fig. 7), and sections of it will be described anon. This part is a 
fringed median projection, uniting the right and left vela (vl. ), parts that are found 
in the newly-hatched embryo, dividing the “ stomodseum ” from the “ archenteron ” 
(Balfour, ‘Comp. Emb.,’ vol. ii., p. 74, fig. 42, v.). I have given a diagrammatic 
figm’e of the velum in the Ammocoete (Plate 25, fig. 10, vl.). For a description of these 
parts the reader is referred to Professor Huxley’s paper (“ Cranio-facial Apparatus of 
Petromyzon,” p. 420). This curious little frame is composed mainly of two crura of 
hard cartilage, united in front by a band of soft cartilage, which sends out three pairs 
of filaments, and an odd one in the mid-line. These are all sinuous or ^-shaped ; the 
two outer threads pass across and are attached to the cerato-hyals ( c.liy.), in front of 
their junction with the epi-hyals (e.hy.); these latter are seen as cut across in the figure. 
The inner of the paired threads is the longest, right and left; the others are 
nearly of the same length. 
The hard crura are bent out, like knees, and these are pedate behind, with a heel of 
soft cartilage. 
5. The labial cartilages. 
The upper lip, which was a hood in the embryo and larva (Plate 8, figs. 1-6), 
overlapping and far outreaching the short, transverse lower lip, has grown very much, 
but not in the same degree as the lower lip (Plate 8, figs. 10-16 ; Plate 18, figs. 1, 
2, 3; and Plate 23, fig. 1). 
The upper lip has acquired a skeleton, such as we find in all the Tadpoles of the 
“ Phaneroglossal Anura.” There are five upper labials in this type, and the median 
is a shield-shaped piece, hollow below, convex above, and overlapped by the cornu 
trabeculae (u.l 1 ., c.tr.); these two parts are the so-called “anterior” and “posterior 
dorsal cartilages.” Under the lower edge of the great median upper labial, right and 
left, there is a small, bent, bluntish style, the “ antero-lateral upper labial ” (u.l 2 .). 
Behind the large piece, right and left, there is a reniform plate of cartilage, much 
larger than the styloid piece, which, lying obliquely, helps to fill up the space between 
the two dorsal cartilages and the prepalatine ; this is the “ postero-lateral upper labial ” 
{u.l 3 .). 
In the larva of the “Anura” (see Phil. Trans., 1881, Part I., var. loc.) these car¬ 
tilages never quite agree with those of the Lamprey, although they are manifestly 
homologous. There may be one, two, or four, and they are evanescent in those types, 
MDCCCLXXXIII. 3 I 
