26 
MR. W. K. PARKER ON THE STRUCTURE AND 
outwards and forwards ; all the other clefts (cl' 2, 3 ~ 5 .) have the same form and direction, 
but they are larger, and open externally, although covered afterwards with the oper¬ 
cular skin, which only opens on the left side. The second cleft (cl 2 .) is between the 
hyoid cornu and the first branchial pouch ; it runs into the floor some distance from the 
hyoid facet. 
Between the articular surfaces of the free mandibles (rah.) the mucous membrane 
is raised into two crescentic folds ; these are the lateral rudiments of the tongue (tg.); 
if these lobes simply grew forwards the Frog would have a bilobate tongue with its 
free ends growing forwards—-it would be protero-glossal. 
Between these lobes there are several large papillae; behind them the mucous 
membrane thinly veils the hyo-branchial arches (Plate 1, fig. 4, and Plate 2, fig. 8), 
At the mid-line there are, behind the papillae, first the basi-hyal (b.hy. ) and then 
the double basi-branchial ( b.hr.) ; whilst on each side are the broad hyoid cornua (c.hy.) 
and the sub-median and lateral elements of the branchial arches ( li.br .) and its rays 
—all that exists of the endoskeletcil framework of these parts. Thus in the larval 
condition the Frog lias the dorsal portion of its hyoid and branchial arches suppressed : 
four large “ extra-branchials ” (Plate 1, fig. 4, br.p. ; and Plate 2, fig. 8, ex.br 1-4 .) 
supplement the deficiency, and those bars, the first and last of which are cochleate, 
are homologous with half of the branchial basket-work of the Lamprey, namely, with 
the four bars of its framework from the first to the third pouch inclusive. 
In his valuable paper on the Lamprey (Journ. of Anat. and Phys., vol. 10, pp. 412- 
429), Professor Huxley does not notice the existence of arches homologous with the 
proper branchials of Selachians, Ganoids, and Teleostei; but his description of the cor¬ 
respondence of these parts with those of the Lamprey must be given here : — 
“ In the present stage the branchiae of the Tadpole are, as is well known, pouches, 
which present no superficial likeness to the branchial sacs of the Lamprey. A septum 
extends inwards from the concave face of each branchial arch, and the septa of the two 
middle arches terminate in free edges in the branchial dilatation of the pharynx. 
Vascular branchial tufts beset the whole convex outer edge of the branchial arch, and 
are continued inwards in parallel transverse series of elevations, which become smaller 
and smaller towards the free edge of each septum, near which they cease. 
“In the young Ammocoete the septa of the branchial chambers similarly bear vascular 
processes, which are first developed close to the external branchial aperture, and thence 
extend inwards transversely.* 
* In a note here, Professor Huxley remarks: “If tlie first-formed long branchial filaments of tlie 
Ammocoete projected tlirongli the small gill-clefts outwards instead of inwards, they would resemble the 
first-formed ‘ external gills ’ of Elasmobranchs. And this difference of direction seems to indicate the 
solution of the difficulty, that external gills, which are so generally developed at first in HUasmobrancMi, 
Ganoidei, and Dipnoi, are apparently wanting in Jfarsipobranchii.” I may add to this note an observation 
of my own illustrative of the writer’s remarks, namely, that in the larva of Dadylethra there are no 
branchial filaments growing from the outer face of the branchial pouches (see “ Batrachia,” Part II., 
Plate 58, fig. 1.) 
