OF THE MARSIPOBRANCH FISHES. 
431 
middle of the large labial muscular mass outside the cartilage ( s.cl .), the section of 
which is crescentic; the annular cartilage gives attachment to these fibres, above ; its 
upper edge, only, is free. The lower cartilage is called by Schneider (see his plate 8, 
fig. 1, Cel.) “ Cartilago-dentalis ” (“ Knorpel fur die seitlichen Zahne ”). I have not, 
elsewhere, seen this cartilage noticed, and my sections created for a time a difficulty : 
dissection of the suctorial disk, both of the young P. marinus and of the adult P. 
fluviatilis, gave the explanation. There is not merely one lateral loiver labied on each 
side, but three (Plate 18, fig. 1, l.l 2 " 4 .) ; they are small, irregularly oval patches of hard 
cartilage, lying in a profusion of large-celled simple cartilage, quite like that seen in 
the larva of Dactylethra and intermediate between the “vacuolar tissue” of the 
notochord (and of the huge basi-branchial bar of the Myxinoicls), and the ordinary soft 
cartilage of Marsipobranchs generally. This large-celled simple cartilage fills the 
cavities of the horny teeth, and is, indeed, the kind of pithy connective tissue which 
goes to fill the interspaces of the higher kinds of tissue in this large spongy disk.* 
'2nd Section (Plate 20, fig. 2). —The first “lateral upper labial” ( u.l".) is now cut 
across under the median plate {u.l'.) ; the annular cartilage (l.l 1 .) is mow lower and more 
bent outwards, and the lateral lower labial (l.l 3 .) is smaller. The fore end of the 
tongue and its teeth (tg., l.t.) is shown in the arched oral opening ; here the roof of 
the oral opening is seen to be formed by the great upper labial, but the disk grew some 
distance in front of this part. 
3rd Section (Plate 20, fig. 3). —In this section the remarkable imbrication of the 
cartilages is shown, and, looking at the side view (Plate 18, fig. 1), we see what parts 
have been cut across. The large overlapping trabecular cornu ( c.tr .), the great size of 
which seems more remarkable in the sections than in the dissections, is thin here 
at its fore edge, well arched, and is much wider than the great azygous labial. That 
cartilage (u.l'.) is very similar in its sections for some distance ; it is too much arched 
to be quite concentric with the great cornu, and its edge is thickened or ribbed, and 
turned slightly inwards. Following the line of its incurvation below, we see the small 
front lateral style (u.l”.), sharp above and rounded below. Here, in the upper part of 
this large portico, under the median labial, we see again the front outline of the great 
broad-ended tongue (tg.), which widens upwards, and has a concave upper outline. 
On each side of the severed jDart of skin, at the base of the tongue’s tip, the annular 
cartilage (l.l 1 .) is cut through as it thickens towards its hind part; its section is lobu- 
* Whilst describing these sections of the disk, it may be well to say that it is formed by a great hy¬ 
pertrophy of the lower lip, which grows forwards, closes over the narrowed oral opening, and unites above 
that opening with the upper lip (see Plate 8, figs. 11-13). Hence the cartilages behind the disk lie in 
the substance of the chin and throat, and evidently do not belong to the labial category. The cartilages 
now referred to are the “distal mandibulars,” single and paired. The five cartilages under the cornu 
trabeculae are formed in the upper lip, which is a large hood from the first (Plate 1, figs. 1—3). The 
upper and lower lips of the Lamprey are now seen to be much more (vertically) symmetrical than they 
seemed to be; above, there is one main azygous piece and two pairs of lesser pieces; below, one main 
azygous piece and three pairs of subsidiary pieces. 
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