x RESPIRATORY ORGANS 293 
laminae, with wavy, crenulated margins, attached by a common 
bony base to the upper extremity of the fourth branchial arch, 
and enclosed in a special dorsal enlargement of the branchial 
cavity. The vascular membrane which invests the laminae is 
abundantly supplied with venous blood by a branch of the fourth 
afferent branchial artery, the equivalent efferent vessel joining 
the dorsal aorta. Essentially similar organs are found in several 
Fia. 169. 
scandens, exposed by the removal of 
the greater part of the operculum. 
b.a’, First branchial arch; /.0, laby- 
rinthiform organ ; op, operculum ; sé.c, 
supra-branchial cavity. 
Labyrinthiform organ of Anabas 
genera of Osphromenidae (e.g. 
Polyacanthus, Osphromenus, and 
Trichogaster). A simpler form 
of respiratory organ of some- 
~ Fic. 170.—Supra-branchial cavities of Ophio- 
what the same type occurs 1n cephalus. Ventral view, as seen after 
c A a the removal of the ventral halves of the 
the Indian family Ophiocepha- branchial arches. 6.a!-4, The first four 
lidae In these Fishes there branchial arches ; 0.c, roof of oral cavity ; 
3 : oes, oesophagus ; p.t, pharyngeal teeth ; 
18, on each side, an accessory sb.c, left supra-branchial cavity; v,/; 
branchial cavity, situated above Dies the lining membrane of the 
-that which contains the gills, 
but freely communicating with it (Fig. 170). The cavity is 
lined by a thickened and puckered vascular membrane, but other- 
Wise contains no special respiratory structures. 
In the Siluroid genera Clarias and Heterobranchus the accessory 
organ takes the form of branched, arborescent and highly vascular 
structures, developed as outgrowths from the dorsal extremities 
of one or two branchial arches, and enclosed within a posterior 
and dorsal expansion of the proper branchial cavity (Fig. 171). 
1 Hyrtl, Sitz. d. k. Akad. Wiss, x. 1853, p. 148. 
