28 
MR. W. Iv. PARKER ON THE STRUCTURE AND 
and the long, precocious, filamentous gills of the embryo Selachian, are, like gills 
generally, of hypoblastic origin. 
The vertical longitudinal section (fig. 5) may be now described. 
The large upper labial (below c.tr.) is seen in section; it is the “anterior dorsal 
cartilage ” of J. Muller : below, the lower labial is seen/"' where it joins its fellow to 
form the imperfect “annular cartilage” (see also fig. 4, IX., mk). 
Meckel’s cartilage is seen behind this in the section; it lies in the side of the 
mouth, and its main function is to serve as a suspensorium to the “annular cartilage ” 
(the corresponding half of the imperfect ring) (see also Plate 2, fig. 6, l.l., mk.). 
The raised cushion behind these cartilages is the rudimentary tongue (fig. 4, tg .); 
in the back of this the basal cartilages are placed. 
In most things I agree with Professor Huxley as to his harmony of the Lamprey’s 
and the Tadpole’s mouth. There is some reason to suppose that the antero-inferior 
median cartilage belongs to the mandibular arch. The basi-hyal of Fishes is always 
a “glosso-hyal;” it projects forwards beyond the arch to which it belongs, and so does 
the first basi-branchial. 
Any paired plate of cartilage lying in the same plane, but projecting outwards and 
backwards from the basi-branchial bar (or bars) would be “hypo-visceral;” any rods 
attached above these and lying in the lower half of the sides of the pharynx would be 
“ cerato-viscerals.” 
In the Lamprey (Huxley, op. cit., plate 17, fig. 1) this anterior median cartilage, 
below, is outside the lingual rod, and is probably a basi-mandibular ; and the great 
lingual cartilage ( k .) is an undivided piece, with neither osseous nor fibrous segmenta¬ 
tions, and is evidently an intra-visceral element. 
In the Tadpole (Plate 2, fig. 8, b.hy.) the anterior basal piece does not chondrify 
until metamorphosis takes place ; it is a thick, narrow, conjugating band, composed 
of large cells of simple cartilage. 
But the basi-branchial of the Tadpole ( b.br .) is an oval mass of cartilage, with a 
hinder bud that grows downward beneath the large hypo Branchial plates ( li.br .) ; this 
bud does not become a separate second basi-branchial. These two semi-distinct 
rudiments do not represent more than the end of the long lingual cartilage of the 
Lamprey; and if that fish had paired cartilaginous plates lying on the same plane as 
the lingual cartilage and attached to its sides, behind, they would be hypo-branchial 
plates, for they would belong to the inner category of cartilages, and not to those 
forming the branchial basket-work. 
In the Tadpole the heart (fig. 5, h.) is roofed over by the “ hypo-branchial” plates, 
and the edge of the “inferior velum” (fig. 4, l.v.) is seen completing this roof and 
also covering the inner branchial openings in front. 
Where the right and left vela unite at the mid-line, there they are directly in front 
of the larynx (lx) ; afterwards, the hypo-branchials become the “ thyro-hyals.” 
* The inner face of the lower labial is lettered mk., by mistake, in Plate 1, fig. 5. 
