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 



Fig. 169. — Labyrinthiform organ oiAnabas 

 scandenSj exposed by the removal of 

 the greater part of the operculum. '^ 

 h.a'. First branchial arch ; l.o, laby- 

 rinthiform organ ; op, operculum ; sbx, 

 supra-branchial cavity. 



genera of Osphromenidae (e.g. 

 Polyacanthus, Osphromenus, and 

 Trichogaster). A simpler form 



of respiratory organ of some- ^,,,,170 _g^p^^_,^^.^^^y^i^^^iy33„f Oj^to- 

 what the same type occurs in 

 the Indian family Ophiocepha- 

 lidae.'' In these Fishes there 

 is, on each side, an accessory 

 branchial cavity, situated above 

 that which contains the gills, 

 but freely communicating with it (Pig. 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 Reterohranchus 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. 



ce2^halus. Ventral view, as seen after 

 the removal of the ventral halves of the 

 branchial arches. b.a?--\ The first four 

 branchial arches ; o. c, roof of oral cavity ; 

 oes, oesophagus ; p.t, pharyngeal teeth ; 

 sbx, left supra - branchial cavity ; v.f, 

 folds of the lining membrane of the 

 cavity. 



