560 
ME. W. K. PAEKEE ON THE STEUCTUEE AND DEVELOPMENT 
embraces the condyle of the mandible ; externally, it seems to lie in it, the hinder part 
of the articular condyle being somewhat hollowed for the outer lip of the quadrate. 
The other five arches, notwithstanding their size and solidity, are entirely cartilaginous 
(Plate 25. fig. 5, and Plate 26. fig. 5) ; they are for the most part gently arched and 
oval in section. 
In degree of transverse segmentation they are intermediate and between those of the 
Selachian, where the hyo-branchial series has most superimposed pieces, and those of 
the larval Batrachian, which has fewest. 
In the latter, indeed, the true (inner) branchial arches are distal rudiments of the cerato- 
branchial pieces, attached to hypobranchial plates; in Selachians (Gegenbaur, op. cit. 
plates 14-19) there is great subdivision of the bars and permanent separateness. 
In these latter types there is so much regularity of these numerous segments, where 
the hyo-branchial cage is most highly specialized and has its most massive development, 
that it can be used as an exemplar and rule both for comparison and for nomenclature. 
In the Osseous Fishes (see “ Salmon’s Skull,” plate 88. fig. 9) these parts are still 
more specialized by bony deposit, pharyngeal teeth, &c. ; but the segments easily take 
the same names. The small distal hypohyal ( h.hy .) of Siredon has no representative 
in its branchial arches, and in the hyoid arch the upper piece or hyo-mandibular is 
entirely suppressed. 
The cerato-hyal (with the small distal segment) corresponds to the free mandible, to 
which it is attached by the mandibulo-hyal ligament ( m.h.l .) ; the hyoid cornu is also 
strapped to the suspensorium by the hyo-suspensorial ligament ( h s.l .). 
The next two arches have a suspensorial piece more than twice the size of the lower 
or free cornu ; the next two have no lower segment. In the two large front arches even 
there is therefore no hypobranchial below nor pharyngo-branchial above. The latter 
part is represented by a sort of hammer-head to the two middle bars, the first and fourth 
bowing towards this transverse process (Plate 26. fig. 5, e.br.). The two cerato- 
branchials (e.br. 1, 2) are stout, straight styles, the first articulating below to the sides 
of the basal piece behind, and the next to its end. The three first epibranchials have a 
long, single, feather-like gill (e.br.) attached outside the upper third ; these are about 
the length of the bar from which they arise. The first bar has a snag near where 
the gill is attached. Tooth-like processes interdigitate between the arch and form 
the usual gill-colander in this group. The first basibranchial {Jj.br. 1) is a long, 
oval, thick, high cartilage, rounded in front, and having the hyoid arch attached 
to it by ligaments. It serves as a conjugational piece for the hyoid and the first two 
branchial arches. The second basibranchial (b.br. 2) has no arch attached to it ; it is 
compressed in front and flat behind, where it becomes spatulate. It is twice as long as 
the first, and it is the homologue of the so-called “uro-hyal” of the bird*'. 
* It should he borne in mind that the suspensorium of the mandible, like the hyo-mandibular (with its 
symplectic peg), answers to the pharyngo- and epibranchials together. The mandible, the hyoid cornu, and 
the cerato-branchials also correspond. 
